Technology Trends of Catalysts in Hydrogenation Reactions: A Patent Landscape Analysis

Abstract The purpose of this review is to present an overview of the patent landscape for catalysts used in hydrogenation reactions. Based on patent data extracted from PatBase®, we use predefined patent classifications as well as a keyword‐based search for our analyses. The results indicate that the number of patent families that protect heterogeneous catalysts grows twice as fast as that for their homogeneous counterparts. Furthermore, the data show a shift towards abundant and non‐toxic elements in heterogeneous catalysis, while the noble metals continue to dominate the patent landscape of homogeneous catalysis. A subsequent geographical analysis reveals that the high growth rates in heterogeneous catalysis, especially for nickel and iron, are driven by China. Conversely, patenting activities with regard to homogeneous catalysts mainly take place in the USA, the EU, and Japan. The subsequent keyword‐based search illustrates the continuous industrial relevance of enantioselective hydrogenation and transfer hydrogenation, as well as the rapidly increasing body of patents in hydrodeoxygenation. Setting these finding into context, we present and apply two concepts that are commonly used in patent analyses, namely the technology life cycle and the S‐curve. We conclude that hydrogenation catalysis has not reached its peak economic relevance yet and will continue to spark valuable patents and innovations in the future.

Abstract: Thep urpose of this review is to present an overview of the patent landscape for catalysts used in hydrogenation reactions.B asedo np atent data extracted from PatBase,w eu se predefined patent classifications as wella sakeyword-based search for our analyses.T he results indicatet hat the number of patent families that protect heterogeneous catalysts grows twice as fast as that for theirh omogeneous counterparts.F urthermore,t he data show as hift towards abundanta nd non-toxic elements in heterogeneous catalysis,w hilet he noble metals continue to dominatet he patent landscape of homogeneous catalysis.Asubsequent geographical analysis reveals that the high growth rates in heterogeneous catalysis, especially for nickela nd iron, are driven by China. Conversely,p atentinga ctivities with regard to homogeneousc atalysts mainly take place in the USA, the EU,a nd Japan.T he subsequent keyword-based search illustrates the continuous industrial relevance of enantioselective hydrogenation and transfer hydrogenation, as wella st he rapidly increasing body of patents in hydrodeoxygenation. Setting these finding into context, we presenta nd apply two concepts that are commonly used in patent analyses,n amely the technology life cycle and the S-curve.W ec onclude that hydrogenation catalysis has not reachedi ts peak economicr elevance yet and willc ontinue to spark valuable patents andinnovations in the future.

1I ntroduction
Catalysis is ak ey technology in chemicalsa nd pharmaceuticals.I ti se stimated that for over 90% of all chemical products, the production process involves at least one catalytic fabrication step, [1] andn ot seldom, this is ahydrogenation reaction.
First defined by Berzelius in 1835, later refined by Ostwald,acatalyst is ac hemical entity that speedsu p ac hemical reactionw ithout being itself changed in the course of the process. [2][3][4] It does not influence the thermodynamics of the overall reactionb ut permits a previously inaccessible reactionp ath. This can lead to ad ramatici ncrease in the reaction ratea nd enables chemical transformationst hat are otherwise not feasi-ble.T he advancesi nt he theory and applicationo ft he concept of catalysisi nt he 19 th century culminated in the Nobel prize for WilhelmOstwald in 1909. [4] On ag enerall evel, catalysts are characterized as homogeneous or heterogeneous,d epending on whether they exist is the same phase or in ad ifferent phase than the reactants.Ahomogeneous catalyst is in most cases as oluble chemical entity that speedsu pt he reaction of reactantsi nt he same,t ypically liquid, phase. Prominent examples include molecular transition metal complexes such as Wilkinsonsc atalyst, Noyoritype catalysts,C rabtreesc atalyst, and Schrock-Osbornsc atalyst, among others.H eterogeneous catalysts are in most cases solids,o rm ixtures of different solid components that are not in the same phase as Marius Stoffels received a PhD from the Westfälische Wilhelms UniversitätM ünster under the supervision of Prof.J ensL eker. His research is positioned at the nexus of science and business. Currentr esearchi ncludes the impact of digital technologies on value creation in the chemical and pharmaceutical industry.
Thomas Hamadi is Innovation and Patent Manager at InfineonT echnologies AG and obtainedh is PhD from the Instituteo fB usiness Administration at the Department of Chemistry and Pharmacy,U niversityo fM ünster. His researchf ocus is on patent analysisa nd innovation management in hightech industries.
Jens Leker is aF ull Professor of Business Administrationi n the Natural Sciences at West-fälischeW ilhelms-Universität Münster. He is Editor-in-Chief of the Journal of Business Chemistry and his research includesc orporate strategy, patent analysis,t echnology foresight, andi nnovation management in researchintensivei ndustries.
Felix Klauck studied chemistry at the University of Cologne and the RWTH Aachen University. In his Master studies he joined the group of Prof.J .C .A nderson at the University College Londonf or ar esearch stay. He pursued his doctoral studies with Prof.F .G lorius at the Universityo fM ünster working on metal-catalyzed C À Ha ctivation and photoredox catalysis. After obtaining his doctoral degree in the year2 019 he started working at INEOS Styrolution as aR esearch Specialist for styrene-based polymers.
Frank Glorius is aF ull Professor of Organic Chemistry at the Westfälische Wilhelms-UniversitätM ünster. Hisr esearch programf ocusses on the development of new concepts for diverse areas of catalysis such as photocatalysis, C À Ha ctivation,s mart screeninga nd data-based technologies,N -heterocyclic carbenes (NHCs) in organocatalysisa nd as surface modifiers and in (asymmetric) arene hydrogenation. the reactants. In this domain, Raneyn ickela nd Pd/C are welle stablished. Ty pically,t he reactantsa re dissolved in al iquid or gaseous phase and are brought into contact with the solid catalyst to effect an increase in reactionr ate. [5] In the chemical industry,t he vast majority of catalytic processes involve heterogeneous catalysts due to their advantage of beinge asily removablef rom the reactionm ixture by physical solid-liquid separation techniques. [6] Heterogeneous catalysts can be distinguished by the fraction of catalytically active material the solid contains.F ull catalysts consist solely of the catalytically active material, whereass upported catalysts also contain other species,w hich may have ac atalytically relevant function but can also merely serve as ac arrier. These two realms of catalysis (homogeneous vs. heterogeneous) require distinct technologies for the preparation, the analysis and the applicationofc atalytic bodies.
In this work, we analyze the patent activity in the field of catalytic hydrogenation. To the best of the authors knowledge, this workc onstitutes the first analysis of the hydrogenation patent landscapet od ate. Patent reviewsh ave been established as at ool for assessingt he status quo of scientific research areas that have accomplishedw idespread industrial application. [7] Prior patent reviews have been conducted for industrially relevant research fields such as biodegradable polymers, [8] lithium ion batteries, [9] ando rganic photovoltaic cells, [10] among others.W hile this type of publication strives to present an overview over technological developmentsi nt he respective field, delivering ad etailedt echnology assessment is often out of scope.T herefore,t he aim of this review is to present ac omprehensive overview of catalyst classes and their evolution for the field of catalytic hydrogenation.
Theh ydrogenation reaction, i.e., the addition of dihydrogena cross an unsaturated moietyo rafunctional group in am olecule,i sf requently applied in the chemical industry.O ften,t he reactioni so nly feasible in the presence of ac atalyst (stoichiometricr eductions by diimide species are known, [11] but are of low economics ignificance). Even though frustrated Lewis-pair species have also been evaluated as hydrogenation catalysts, [12] the importance of transition metal catalysts outweighsthese recent developments.
Thep aper is structured as follows: As hydrogenation can be effected by both homogeneous and heterogeneous catalysts,w es tart by presenting examples for these reactiont ypes,f ollowed by ab rief introduction into the use of patent analysis. Ther esearch design will then be explained and the technological landscape among catalysts in hydrogenation will be presented. Finally,w ec omplement the classificationbased analysis with ak eyword-based approach.

2T heory 2.1 Introduction to Hydrogenation
Hydrogenation describes ac hemical reactiont hat involvest he addition of dihydrogen (H 2 )t oa nu nsaturated moiety (see Scheme 1). Thep roduct of this type of reactioni samolecule that bears two or more additional hydrogenatoms in its molecular architecture.
Thed evelopment of catalytic hydrogenation reactions is an outstanding examplef or how chemical research influences industry practices and, subsequently, has been honored with two Nobel prizes (i.e., Sabatier 1912, Knowlesa nd Noyori in 2001). [13][14][15] Today, also represented by the large number of patents filed, catalytic hydrogenationr eactions are used extensively throughout the chemical industry.T he examples presented in the following underline the essential role of hydrogenation reactions for the production of commoditya nd specialty chemicals.

Benzene Hydrogenation to Produce Cyclohexane
Thec atalytic heterogeneous hydrogenation of benzene to cyclohexane is an exampleo falarge-scale hydrogenation reactioni nt he production of commodity chemicals.C yclohexane is ac yclic hydrocarbon that is also an intermediate for the production of e-caprolactam. This compound is required for the production of Nylon fibers and resins (see Scheme 2). [6] Ty pical reaction conditions involve the applicationo fasupported (heterogeneous) nickelc atalyst at temperatures between 170 and 230 8 8Ca tahydrogenp ressure of 40 atm. [16] Scheme1.Exemplary,s chematic representation of olefin hydrogenation. Other functional groups are also included in the analyses.
Scheme2.Industrial process of catalyticbenzene hydrogenation in the value chain of Nylon production.

Production of l l-DOPAb yE nantioselective Catalytic Hydrogenation
An instructive example for the industrial application of catalytic homogeneoush ydrogenation is given by the production of l-DOPA, ad rug usedt ot reat Alzheimersd isease.T he drug molecule bears as tereogenic center so that imagea nd mirror image of the compound are not superimposable (Figure 1). The two species are referred to as enantiomers andh ave different effects on the human organism, even though most physical properties are the same.S ince only the l-enantiomer exhibits the desirable activity,amethod for the selectiveproduction of this enantiomerwas required ( Figure 1). [17] In the 1970s,M onsanto patented ap rocess for the enantioselective production of l-DOPA. Thei ndustrial process gives access to the l-enantiomer selectively by aid of ah omogeneousr hodium-catalyzed hydrogenation of the precursora cetamidocinnamic acid derivative (Scheme 3). [18]

Introduction to Patents andP atent Analysis
Patents are am ajor force of competitive advantage in knowledge-intensive industries such as chemicalsa nd pharmaceuticals.T heyc onstitute af orm of intellectual property and grant the patentso wner the right to exclude others from exploiting an invention in one or more geographical areasf or ad istinct period of time. Furthermore,p atents are an importanti ndicator of technological evolution. [19] Fort his reason,i ti sw orthwhile to analyze the patent landscapes of technology areas.
In ordert oq ualify for patent protection, an invention must meet the following three core criteria besides its general patentability:n ovelty (not "state-ofthe-art"), usefulness (susceptible of industrial application),a nd non-obviousness (involvemento fa n" inventive step"). [20] Patentp rotection for as pecific geographical region is granted by the respective national or regional patent office,f or example,t he United States Patenta nd Tr ademark Office (USPTO) or the European Patent Office (EPO). Thedate of the initial patent application is called the priority date, also referredt oa st he priority. After this initial application, further national, regional andi nternational filings with referral to the priority can be made.P atent applications that refer to the same priority are called patentfamilies. In most countries,the invention is protected for 20 years and the patent is publicly disclosed after 18 months.
Patents are ar elatively reliables ource of technical information, since they are typically subjected to thorough legal examinations.A lthough it is known that single patents may contain erroneous information, and different patenting strategies exist, the bodyo f the patent itself -a sw illb eu sed for our analysescan be regardeda so ne of the most reliables ources of publiclya vailable technical information on hydrogenation catalysts. [19] Consequently,t he analysis of patents is aw ell-establisheda pproach for assessingt echnological change and forecasting the trajectorieso f emerging technologies. [21][22][23][24] As uitable indicator for the developmento fp atent activity is the number of patent applications over time. [19,20] In this context, the technology life cycle concept and the S-curve concept have been established as two theoretical lenses.A ccordingt ot he technology life cycle -a si ndicated by the dotted line in Figure 2the evolution of patent activity for anyt echnology  goes through three stages. [19] These include first, an "emerging" phase with acceleratingp atentinga ctivities,s econd, as ubsequent consolidation period coined by as loweri ncrease or even ad ecline in patents,a nd third,am arket penetration phase in which activities reach theirp eak before they slowly decline again. Furthermore,a nS -shaped (sigmoidal) relationship of technological performance (or cumulative R&D expenditures) over timeh as been reported (see Figure 2). [9,19] Accordingt ot his concept, the technologicalp erformance equally runs throughd ifferent stages.I nt he emerging stage,t echnologicalp erformance is low andm ost effort is devoted to basic research. Thef ollowing growth stage is characterized by an accelerated growthr ate (pacing technology), while in the maturity stage performance improvements flatten out (keyt echnology). In the saturation stage,the technological performance starts to stagnate and furthert echnological performance improvements require high R&D efforts (base technology). Since technological performancei mprovementsa re often costly to unlock in the maturity and saturation stage, further R&D investments might only pay off for firms with sufficient production scales. [19] While the number of patent applications is an indicator for the industrial interest in ap articulart echnologicalf ield, [25] it does not givea ny information about the economic quality of the patents.F or the evaluation of the patent quality,w eu se the share of triadic patents as an indicator, which is ac ommon approach for assessingt he economic value of as pecific technologicalf ield. [8,25] Tr iadic patents are patents that are registereda tt he patent offices in the USA (USPTO), in Europe (EPO), andi nJ apan (JPO). [26] Thel ogic is that if ap atent has been filed in these three strong economies,i tm ust be of high industrial relevance, which is also referred to as the patentsq uality.

3R esearch Design
Fort his analysis, the online patent-database Pat-Base was used. This database providesa ccess to patent documents from over 100 issuing authorities worldwide andc ontains more than 47 million patent families. If patents contain common priorities with other patents,P atBase groups them into families. These extended familiesa re used by the European Patent Office (EPO)a nd have the advantage of deduplicated andp re-grouped results.
In order to create ac omprehensive ande xhaustive dataset for subsequent analysis, we followed the proceduresd escribedi np rior literature. [9] Specifically,w e used the International Patent Classification (IPC) and Cooperative Patent Classification (CPC)i nc ombination with as earch term in the title,a bstract, and claims fields.B asedo nt heir content, patents are equippedw ith at least one but usually several of these IPC/CPC classifications to increase their retrievability andg roup them into technologically related categories. TheC PC system is the result of aj oint harmonization efforto ft he European and US patent offices.I tw as recentlyi ntroduced and allowsamore detaileds earch among technologiesc ompared to the IPC system. [27] Classification codes are based on textual contents and provide more objectivityi np atent searches.C lassification systems are,h owever, limited in their depth of detail and degree of differentiation. [9,28] Therefore,t hey are able to provide ag eneral overview of the developmentsi nt he field and can be expanded by more specific analyses or distinct research areas.
Acknowledging these limitations,w eu sed ac ombined classification-a nd keyword-baseda pproach of IPC and CPC codesa nd precise keywords. [9] Boolean operators as well as truncation were included in this patent search. Thek eyword search wase ither based  [19] on the full text (FT) or on the title,a bstracta nd claims (TAC)o fe achpatent document.
To furtherd istinguish between heterogeneous and homogeneous hydrogenation, we used several IPC and CPC codes,w hich allow ad istinction of the catalyst nature and phase of the catalytic body.F urthermore,i nt he case of homogeneoush ydrogenation, we also excluded all supported reactions and all patents which were found to be in the field of heterogeneous hydrogenation. Hence,w eu sedt he clearly defined IPC andC PC codes to differentiate between heterogeneousa nd homogeneous catalysts.I tm ight occur that some patents describing ah omogeneousc omplex for the reactiono fi nterest actually involve ah eterogeneousa ctive species in the reactiona nd vice versa. However, by checking samples of the respective results manually,w ec onclude that this instance does not threaten the validity of our findings.

4A nalysis and Results
In the following analyses,w ec ategorize hydrogenation catalysts according to their IPC and CPC codes and discuss developments among the different types of catalysts employed. First, we show the overallp atenting ratei nc atalytic hydrogenation, and in heterogeneousa nd homogeneoush ydrogenation specifically. Then, we present major developments in industrial R&D among the manufacture of catalysts,t he catalysts themselves,a nd catalyst investigation andfurther manipulation.

Developments in the Field of Catalytic Hydrogenation
Starting with ag eneral overview,F igure 3p resents annual patent activitiesi nt he field of catalytic hydrogenation.P robably one of the first and stillo ne of the most important processest hat involve catalytic hydrogenation is the Haber-Bosch process introduced into chemical production in 1913. Ammonia is produced by the catalytic addition of hydrogent on itrogen from air over ah eterogeneous catalyst. Withoutt his process,t he tremendous need of ag rowing population for synthetic fertilizers could not have been satisfied. [29] Figure 3s howsagrowthi np atent family applications for hydrogenation from 1925 onwards.[ NB: In this further analysis, patent family applications are termeda sp atent families.] In terms of the technology life cycle,t his is the emerging phase (I)d uring which hydrogenation catalysts started to become utilized in the chemical industry.I nt his emerging phase,w hich lasted until around 1960, ag rowthi np atent activity can be observed and more companiess tarted to enter this technologicalf ield. From then on the patent ac-tivity stayed mostly constantu ntil 1993, indicative of ac onsolidation phase (II). Here,R &D expenditures are reduceda nd efforts refocused based on the experience in the applicationo fc atalytic hydrogenation. Beginning in the mid1 990s,arapid growth in patent activity is observed, indicating the transition into the market penetration phase (III). Accordingt ot he Scurve concept,c atalytic hydrogenation technologies can be considered to be in the endo ft he growth stage,w here the competitive impact is high and the integration into process technologiesiso ngoing. [19] In this analysis,w ef ocus on the nature of the precatalysts,s ince they are clearly distinguishable as heterogeneous or homogeneous. As shown in Figure 3, heterogeneous hydrogenation accounts for ah igher patent activity compared to homogeneoush ydrogenation. Furthermore,l ooking at the development of the annual number of patent families, the curve for heterogeneous hydrogenation follows the same shape as the curve representing catalytic hydrogenation. This resulti sn ot surprising,a st he heterogeneous nature of solid catalytic bodies inherently possesses advantages over homogeneousc atalysts.M ost notably,t hey are easily separable from the reactionm ixture and therefore reusable, they enable ac ontinuousp rocesses design with as tationary catalyst, and eventually show superior economic properties.T he overallh ydrogenation curve also includes patents that are not in one of these clearly defining classes,s ot he homo-Figure3.Annual patenta ctivities in the field of catalyzed hydrogenation, heterogeneoush ydrogenation, and homogeneous hydrogenation reactions.D ue to the strict parameters appliedf or the homogeneous/heterogeneous classification, the two do not add up to the overall curve. geneousa nd heterogeneous curves do not add up to the overallc umulated number of patents in the field of catalytic hydrogenation.
To give am ore detailed analysis of the patent landscape in catalytic hydrogenation, we differentiate the field of catalytic hydrogenation according to three different research fields:( i) fabrication of catalysts,( ii) catalysts,a nd (iii)c atalyst investigation and further manipulation. In the next section, the fabrication of catalysts,w et ake ac loser look at catalyst carriers and the preparation and protection of catalysts.A fterwards,w ed iscuss developmentsa mong different catalysts materials,s uch as Raney-type catalysts,m etal oxides,a nd coordination complexes.H ere,w em ake a detaileda nalysis of the different metals used in oxides and coordination complexes andt heir economic and technological quality.W et hen presenta no verview of the patent landscapes for the catalysts physical properties andt he regeneration of catalysts.A ll of these research areasa re classifieda ccording to IPC and CPC codes, which allow ad istinction of these fields.F igure 4s hows an overview of the three different research areas among catalysts and the underlying International PatentClassifications.

Preparationo fC atalysts
Thep reparation of heterogeneous catalysts often includesc hallenging procedures to obtain ar eproducible catalytic body.I nm any cases,t he production procedure for ah eterogeneous catalyst critically determines its selectivity and activity.W hile the prepara-tion of catalysts was primarily done in at rial-anderror process up until the 1970s,i th as evolved into a dynamic and economically important science that requires an interplay between many disciplines within chemistry and material sciences. [30] Figure 5r eveals that within the domain of catalyst fabrication, the preparation of catalysts yields more patents than the related topics of catalyst carriers and protection of catalysts.F urthermore,p atentinga ctivities in the field of catalyst preparation show as ignificant increase starting in the mid 1990s,t ogether with the overall increase in patentinga ctivity already shown in Figure 3. As alreadyp ointed out above,t he preparation of catalysts has been professionalized and connected to other research areasf rom the 1970s, [30]   eventually leading to as teep increase in patents in the 1990s.
In order to better understand the drivingf orces of this increase,w ec onducted am ore fine-grained analysis of the preparation techniques for catalysts that is shown in Figure 6. Ther esults reveal that impregnation as ap reparation method (B01J37/0201) is am ain driver of this increase.I mpregnation describes ap rocess in which as upported catalyst is prepared by exposing the catalyst support to as olution of the active metal component. Them etal is then bound to the surface by ionic interactions or ligation of the metal atom. [31] Examples include the impregnation of Ni on Al as the support to form ac atalyst for the wellknown steam reforming process. [32] Thes econd most found patent classification is the mechanical treatment of solid catalyst bodies (B01J37/0009). These physical treatments involve processess uch as molding, pressing, grinding, or granulating of the solids. This procedure influences mechanical stability,a ctivity,a nd the regeneration procedure for catalyst reactivation.T he third most common class in the subgroup analysis was the catalyst preparation by precipitation (B01J37/03). This preparation method can be usedt o fabricate am ulticomponent catalytic body. Ty pically, as olution of the active metal component and the other components is treatedw ith ap recipitation agent, which is often an acid or ab ase.T he precipitate is commonly collected by filtration,d ried, shaped, and calcined to yield the active catalyst. [31] A further subclass for the investigated hydrogenation catalysts is the reduction of the precatalyst (B01J37/ 16), which is often done by using molecular hydrogen.
In that way,t he catalytically active,r educed states of the metal components are achieved. [33] Thef ifthm ost found subclass,h eat treatment (B01J37/08), can be viewed in ag eneralm anner and describesa ll processes in which acatalyst is treated with heat during fabrication. Thec lass "Sulfiding" (B01J37/20) was the sixth most found class in the subclass analysis.I nt he petrochemical industry,t he raw natural gas-oil contains considerablea mounts of sulfurc ompounds that can poison catalysts of downstream processesa nd be detrimental to the performance of end-product fuels. [34] Therefore,t he hydrodesulfurization( HDS) process is employed to remove sulfur from the crude oil by treatment with molecular hydrogen( i.e. ,b yh ydrogenation). To obtain highly active catalysts for the HDS process,t he catalysts,m ostly NiO or CoMoi n combination with MoO 3 ,a re treated with sulfur-containing compounds to form the respective active metal sulfides. [35]

ProtectionofC atalysts
Fors ome catalyst recipes,t he protection of the catalyst (B01J33) is an important step in the fabrication process.F or example,athin Al 2 O 3 layer between the catalytically active material and the underlying support has been patented for steam reforming reactions among others. [36] Thef unction of this layer includes the minimizationo fs ide reactions,t he reductiono f corrosion, and the reductiono ft hermale xpansion stress. [36] Interestingly, despite its economic relevance in large-scare processes,w eh ave observed only a small number of patents being filed in the domain of catalyst protection.

Catalyst Carriers
Catalyst carriers,a lso known as supports, are substantial components of ac atalyst system, which is why they are listed under their own patent classification (B01J32). It was observed that the patentinga ctivity among catalyst carriers concerning the hydrogenation reactionw as low over the time frame of investigation. Only from 2008i saslight increase in patenting activity observed. Ac arriero facatalyst can be anym aterial that carriest he active catalyst andi tm ay have other functionst han just structural fixation. Analogous to the field of catalyst protection, catalyst carrier materials are probably not explicitly classified.

Metals, Carbon, Oxides andHydroxides
Theh ighest number of patents are included in the IPC codes B01J21 and B01J23, which are analyzed together. TheseI PC classes include elementalf orms of av ariety of chemical entities,a sw ell as the oxides and hydroxides of av arietyo fm etals.N umerous typical heterogeneous hydrogenation catalysts such as PtO 2 andPd/C fall within these categories.

4.3.1.1Supporting Materials
IPC class B01J21 contains catalysts comprising the elements, oxides or hydroxides of Mg, B, Al, C, Si, Ti, Zr or Hf.W hile these elements are usuallyn ot the active components in hydrogenation catalysts,t hey are often used as supports for noble metals to produce an active hydrogenation catalyst or as promoters.T he pure,c atalytically active material -e veni na highly porous form -wouldhave alot of precious material located at the inside andt hus not available as a catalytic entity.F or this reason,c atalytically active material is spread out on as uitable supporting (inactive) material that can increase the contact area of the active sites with the reactionm edium, which greatly improvesthe catalystscost efficiency.Promoters are ingredients that are not catalytically active but enhance ac atalystsp erformance,s electivity,o rl ifetime. [37] Thep atentinga ctivitiesf or elements in the IPC class B01J21 are in decreasing order:A l, C, Si, combinations of Si and Al, and Ti.T hese are typical supporting materials for heterogeneous catalysts, since they are readily available materials.

4.3.1.2Active Metal Components
TheI PC class B01J23 contains information concerning the active metal component of the catalyst. Table 1s hows an overview of the most patented active metal components in this IPC class based on their total number of patent familiesa nd their average annual growthr ate within cumulated patent families for the period 2011-2015.A ll metals show positive growth rates which are,h owever, quite different in their magnitude.P atent family growth rates range from 1.3-9.4%, indicating almosts tagnation for some metals vs. considerable growthr ates of almost1 0% for others.T able 1s ummarizes our findinga mong the heterogeneous metal catalysts classified in IPC B01J23.I nt he table,t he homogeneousc atalyst metal section was derived from the more fine-grained CPC codes (B01J2531 and respective subclasses thereof), which enable ad etailed analysis of complexes with specificc entral atoms.
Theh ighest number of patent families( 1753) was found for Pd. This is not surprising, since Pd is extensively used for hydrogenation reactions andi st herefore of substantial economic and technological interest. Pd on Cisanexample of ahydrogenation catalyst used on industrial and laboratory scales. [38,39] The carbon support in these catalysts is advantageous,a s  it can be burned to recover the precious catalytically active Pd. Ac atalyst containing1 %P ds upported on Ca oxide/Al can be applied for the industrial hydrogenation of phenol. [40] Am edium growth rate of 3.8% was found for Pd in 2011-2015.
Thes econd most patented metal among hydrogenation catalysts is Ni (1106p atent families,B 01J23/755). In recent years,research has uncovered cross-coupling reactions such as the Suzuki-Miyaura reactiont hat use Ni and boron reagents instead of the much more expensiveP d-type reactions. [41] As imilar trend can be observed for the field of hydrogenation reactions, where research strives to harness more abundant elements,s uch as Ni, to replace rare metals. [42] Another typical example is given by the hydrogenation of benzene describedi nS ection 2. Here,asupported Ni oxide catalyst is applied for the hydrogenation of benzene to cyclohexane.O ther significant applications of Ni catalysts are the hydrogenation of fatty acids and vegetable oils and fat hardening. [6] Theh igha verage annual growthr ate in the cumulated number of patent familieso f7 .1% compared to 3.8% for Pd, also shows the industrial importance and increasing interest in Ni as ah eterogeneous catalyst and potential substitute for more expensive catalysts. [41] The third largestg roup of patent familiesw as Ru, Rh, Os, and Ir (1023 patent families, B01J23/46), while Pt (837 patent families,B 01J23/42) is the fourth most abundant metal among the metals,o xides,a nd hydroxides. Pt oxide (also known as Adamsc atalyst) is ac ommon example of aP t-based hydrogenation catalyst. Originally developed to provide ar eproducible catalyst system in the 1920s, [43] Pt oxides are still used in supported catalysts in hydrogenation reactions as are av ariety of Pt-based catalysts for hydrogenation. [44] Theg rowthr ate for the metals Ru, Rh, Os, and Ir amounts to 4.8% and for Pt to 4.2%. Consequently,c omparedt oP d, these metals show af aster increase in interest in the field of heterogeneous hydrogenation, albeit still less than Ni.
Them ajority of metals in this analysis are noble metals.T hus,t he cost efficiency of ap rocess partly depends on strategies to re-use andrecycle these catalytic bodies.
Then ext three most abundant metals among heterogeneous catalysts are Cu (703 patent families), Co (426), and Fe (253). Cu is often usedw ithin Cu chromite catalysts.T hese show ah ighs electivity towards C=Od ouble bonds over C=Cd ouble bonds and are thus applied in the production of fattya lcohols from fatty acids. [45] Co,f or example,c an be usedi ni ts Raneyf orm as ac atalyst to hydrogenate nitriles. [46] Notably,r ecent developments in heterogeneous Co catalysis have emerged, describing av ery active Co catalyst or the hydrogenation of C=Od ouble and C Nt riple bonds. [47] Only recently,aheterogeneous Fecatalyzed hydrogenation of nitroarenes was described, introducing ap romising catalyst system on the basis of this abundant metal that operates under relatively mild conditions. [48] Allt hree metals are less expensive, which makes their use attractivei nt erms of prices for the raw catalyst metals.E specially for Co and Fe,t his attractiveness can be shownb ya ni ncreasing interest in both metals.T heir growth rate for the period 2011-2015 amounts to 6.6% and 9.4%,r espectively,w hich are next to Ni-based heterogeneous catalysts the highest growth rates in this analysis.A sw ew ill see later, these growthr ates are mainly driven by China.
In summary,t he largen umber of patents filed in the domain of active metal components in the context of catalyzed hydrogenationr eactions mirrors the wellknown practical importance of elemental metals and their oxides in the chemical industry.T he amount of patents each yeari sg rowing across all metals considered. Therefore,h eterogeneous catalysts -p recious and non-preciousa like -w illc ontinue to play am ajor role in future chemical hydrogenation reactions.

Coordination Complexes andHydrides
TheI PC class B01J31 describes coordination complexesa nd hydrides and thereby predominantlyi ncludesp atents of homogeneoush ydrogenation catalysts.T he systems usedf or homogeneoush ydrogenation hold af ew intrinsic disadvantages that hamper their applicationi nl arge-scale chemical operations (e.g.,o ften difficult separation from reaction mixture, difficult regeneration of catalysts). Their ability to effect selectivet ransformations,t unability of complexesa nd the ability to hydrogenate substrates enantioselectively underline the importance of homogeneous hydrogenation catalysts for the fine chemical industry. [29] Thes teady increase in patent activity since the 1960s indicates that active industrial research is still in progress to improvee xisting systems and develop new selectivec atalysts.F or am ore detailed analysis,w ef urther investigate ligands and metals used in coordination complexes in the field of catalytic hydrogenation.

4.3.2.1L igand Structures in Homogeneous Hydrogenation Catalysts
On ag eneral level, the properties of homogeneous catalysts are determined by their two constituents: the central metal atom and its ligands.T hese ligands stabilize the complex( inhibiting degradation), tune the electronic properties (making the central atom more reactive), and create suitable surroundings about the reactivec enter by interactions with the substrate (enabling selectivet ransformations). Thus,t he reactivity of ac omplex depends not only on the char-acter of the central atom, but also on its surrounding ligands.T he definedc hemical species usedi nh omogeneoush ydrogenation tend to have consequences for the patent activity on this field. Unlike for heterogeneous catalysts,ahomogeneousc atalystss tructure can easily be determined andt he catalyst species can readily be synthesizedb yacompetitor company in a shorttime. Hence,itseems reasonable to patent acatalyst structure for ac ertain application in order to prevent competitors from applying analogous processes.
Since the ligand structure is of essential importance for the performance of homogeneoush ydrogenation catalysts,amore detailed investigation of patent classifications among coordination complexes was pursued. Thep atent classifications among coordination complexes are organized by the ligand structure employed in the respective coordination complex. We adopted this classification (B01J2531a nd subclasses) to produce the results shown in Figure 8. Figure 8s howst hat phosphorus-containingl igands constitute the majority of complexes applied in patents.T oday there are numerous ligands tructures consisting of ap hosphinem oiety andt hey are widely applied in homogeneoush ydrogenation reactions as modular and tunable entitiesf or reaching the desired reactivity in catalytic systems. [49][50][51] An example is given by the homogeneous enantioselective hydrogenation to produce l-DOPA, as shown above in Scheme 3.
Nitrogen-containingl igands are the second most frequently protectedc lass.I nt his ligand class,c hiral diamines play ac entral role such as in the hydrogena-tion catalysts developed by Noyori (for which he was awarded the Nobel prize in 2001). Today,t hese catalysts are state-of-the-art for the enantioselective hydrogenation of C=Od oubleb onds. [52,53] An impressive example of the systemsu tility can be found in the enantioselective synthesiso ft he antidepressant drug fluoxetine reported by Noyori using chiral diamines as ligands in addition to phosphorus-containingl igands. [54] Unsaturated compounds (cyclopentadienyls,o lefins) are the third most found group of ligands.A lthought hey are sometimese asily replaceable,u nsaturated compoundsm ay substantially tunet he reaction properties of the complex. As an example for this group,c yclopentadienylf ragments are readily found in transfer-hydrogenationc atalysts. [55] Thesea re commonly viewed to be attached to the metal throughout the catalytic process and modifyt he activity and selectivity of ah omogeneousc atalyst species.F ourth and fifth are catalyst species including ligands that contain Oo rS ,a nd carbonyls. Other ligand species play am inor role in homogeneoush ydrogenation catalysis.

4.3.2.2Metal Components in Homogeneous Hydrogenation Catalysts
Foradetailed analysiso fm etals used as ac entral atom in coordination complexes (homogeneous catalysts), we further investigatedt he CPC class B01J 2531, which gives additional information about the centralm etal atom of the coordination complex. Table 1s hows an overview of the most patented metals in this class,b ased on theirt otal number of patent families,a nd their average annual growth rate in cumulated patent familiesf or the period 2011-2015. We find that Rh (457 patent families), Ru (352), Pd (223)a nd Ir (223)a re the most frequently patented metals among homogeneous hydrogenation catalysts.A se xemplified by Wilkinsonsc atalyst, which is an early exampleo favery active Rh complexf or homogeneous hydrogenation and one of the most studied, the field of homogeneousc atalyst metal components was consequently found to be dominated by this metal. [56][57][58] Ru is found as the active metal in Noyori-type catalysts mentioned in the previous section andi sa lso found in great abundance in the patent literature. [52,53] Furthermore,Ir-catalyzed homogeneoush ydrogenation reactions are also well known in the literature,i ncluding enantioselective methods. [59] When looking at the average annual growth rate in the cumulated number of patent families,itbecomese vident that Ru shows the highest growth rate (3.4%)a mong the metals analyzed.P ts hows the lowest growth rate in recent years with 1.3%. When comparing the annual patent growthr ates of hetero- geneousa nd homogeneous hydrogenation catalysts in Table 1, we find that heterogeneous catalysts grow at ac onsiderably higher rate than theirh omogeneous counterparts,w hich is in alignment with the industrial applicability of the reactiont ypes.A lthought he use of base metals woulda lso be highly desirable in homogenous catalysis, and technologies are emerging in this field, [60] the shift towards the use of base metals that was observedi nh eterogeneous catalysis was not found in the patent landscapeo fhomogeneousc atalysis.

Economic and Regional Investigation of Metals in Hydrogenation Catalysts
While the overall technologicali nterest among the analyzed metals in heterogeneous and homogeneous hydrogenation was shown in Sections 4.3.1 and 4.3.2, we further analyze the economicq uality andr egional aspectso ft hose metals.Awell-established patent indicator for the economic quality is the share of triadic patents of at echnology. [61] Tr iadic patents are patents filed in patent offices in the USA (USPTO), in Europe (EPO), and in Japan (JPO). Because these regions are economically strong markets,ahigh share of triadic patents for as pecific technology indicates a high economicv alue for this technology. [61] Thus,w e next investigated triadic patents for all metals analyzed in Sections 4.3.1a nd 4.3.2. Furthermore,w eg ive an overview of regional differencesa mong these metals for heterogeneous and homogeneous catalysts in hydrogenation.
When choosing am etal catalyst for hydrogenation, av arietyo ff actorsh ave to be takeni nto account in order to realize an economically reasonable process: -C atalyst production, i.e., the price of the raw metal ando ther catalyst components,t he preparation process. -C atalyst activity and selectivity,i .e., the ability of the given catalyst to mediate the desired chemical reaction selectively. -C atalyst regeneration, i.e., reusability and processes to reactivate the catalytic body. -C atalyst reproducibility,i .e., the reliability of a given catalyst to give satisfactory outcome of the applied process.
Choosing ac atalyst and especially the central active metal component hast ot ake into account all these factorsa nd often requiresm anaging trade-offs between conflicting dimensions.
Fort he IPC code B01J23, which was earlier determined to predominantly include heterogeneous catalysts,t he majority of catalytic bodies are classified to contain Pd, Ni,R u, Rh, Os,I r, Pt, Cu, Co andF e. This is not surprising since these metals are commonly found in heterogeneous hydrogenation catalysts.
Among these metals,t he difference in the share of triadicp atents,s hown in Table 2, is noticeable. In our analysis,t he highest share of registeredt riadicp atents amountst o3 8% for Ru, Rh, Os,I r, indicating their high economic value in industrial applications.A sa n example from the field of homogeneoush ydrogenations,R hi so ften used as an active catalyst to hydrogenate aromatics, [62] while heterogeneous Ru catalysts can be used for the selectiveh ydrogenation of C=O doubleb onds over C=Cd oubleb onds. [63] An average share of triadic patent familiesa mong the analyzed metals was found for Pd (33%), Pt (35%), Cu (31%), Co (35%) and Fe (30%), while the share of triadic patent familiesf or Ni was found to be significantly lower (26%). Especially in the case of Fe and Ni, a detailedp atent analysis reveals that the main reason for these differences is the substantial increase in patenting activities in China since the 1990s.D ue to the strong increase in the number of patents filed in Chinat here is as ignificant increase in the number of patents in these fields overall, indicating the increasing importance of this region andm arket, eventually reducing the relative importance of the other regions.
Furthermore,t he increasing relevance of Chinaa sa market and innovator in the field of heterogeneous Ni andF ec atalysts is also displayed by the share of patent familiesr egisteredi nC hinaa sapriority country compared to the other regions (see Figure 9). Con-cerningN i, the highest number of patent familiesw as registeredi nC hinaa sapriority country (34% of all patent families), followed by Europe [pleasen ote:f or "Europe", patent families registered in following Table 2. Share of registered triadic patent families for metals in heterogeneousa nd homogeneoush ydrogenationf or the period2 011-2015.

Heterogeneous catalysts Triadic patents
Ruthenium, rhodium, osmium or iridium patent offices as priority country were counted:E PO, Germany,F rance,a nd Great Britain] (28%), the USA (16%), andJ apan (11%). As imilar constellation was observed for Fe,w here 28% of all patent families are registeredi nC hina as ap riority country,f ollowed by Europe (23%), the USA (23%), andJ apan (15%). Specifically,F igure 9s hows that patents in the field of heterogeneous catalysis that are first filed in China focus on the cheaper metals Ni, Fe,C oa nd Cu, while the overall patent activity for the expensivep latinum group metals is considerably lower. Fort he IPC B01J2531, which describes homogeneous catalysts,t he majority of catalytic bodies are classified to contain Rh, Ru, Pd, Ir, Ni, Co,a nd Pt. When comparing these metals with metals used in heterogeneous catalysis, it becomese vident that in generalt he share of triadic patent familiesi sc onsiderably higher for homogeneousc atalysts.T he high share of triadic patents among this subclass mayr eflect efforts to protect the technologiesc lassifiedh ere.A sm entioned previously,t he structure of ah omogeneousc omplex can often be identifieda nd reproduced much more easily than the structure of ah eterogeneous catalyst, and thusm ight be protectedm ore restrictively.T he highest shares of triadic patent families among the homogeneous catalysts were registered for Ru (50%), Ir (48%), and Pd (47%) (see Table 2). ThereafterP t (43%), Rh, and Ni (both 38%) follow,w hile the lowest share of triadic patent families can be observed for Co (29%).
When analyzing the geographicald istribution of patent families among priority countries,t he minor role of Chinaa mong patent applications in homoge-neous catalysts can be seen for the period from 1900-2015 (see Figure 9);o na verage the patent families registeredi na ll analyzed metals amount just to 2%. Thel argestp atentinga ctivity is found in Europe and the USA. On average,b oth regions contributet ogether with 76% of patent familiesr egisteredi nt his field.

Raney-Type Catalysts
As seen in Figure 7t he patent activity for Raney-type catalysts remains on ac onstantly low level throughout the wholet ime frame investigated. Raney-type catalysts,t he most prominent example being Raney nickel, were originally developed to provide ar eproducible catalyst for hydrogenation reactions.R aney nickeli su suallym anufacturedb ym elting Ni and Al to provide an alloy.T he alloy is crushed into fine particles.Subsequently,the Al is extracted by gradual addition of caustic soda solution, leaving ah ighly porous Ni catalyst that is obtained after washing and activation. It is still used as ah ighly active laboratory and small-scale hydrogenation catalyst, however, its high production costs compared to other hydrogenation catalysts hamper its general applicationi ni ndustrial hydrogenation nowadays.N evertheless,t here are still processes that employ these catalyst types. [6] 4.3.5 Catalysts Comprising Elements F, Cl, Br,I,S , Se, Te,P ,N Thec lass B01J27 describes catalysts that contain one of the following elements:F ,C l, Br,I ,S ,S e, Te,P ,N . Most often,t hese elements are addede ither for structural reasons or as promoters.S ince there may be many reasons for adding one of these elements,a structured search of the subclassesw as consideredn ot to deliver further cleari nformation. As can be seen in Figure 7t he patent activity in this class is reasonably comparable to that for the following B01J29c lass, showing increasing patentingf rom around year 2010. It is worth noticing that the patents exemplarily investigated in this class were of heterogeneous nature.

MolecularSieves
Thep atent activity for hydrogenation catalysts on the basis of molecular sieves has experienced ap eak in 1984 and as teady increase since the year2 000( see Figure 7). Molecular sieves (B01J29), including zeolites,a re crystalline porous aluminosilicate materials with small pore diameters of typically < 50 nm. Especially zeolites can react as Lewis acids because of their high Al content. With respect to hydrogenation reactions,t he porous materials can be impregnated with metal hydrogenation catalysts,c reating ab ifunctional catalyst that can not only react to addhydrogen to unsaturated parts of am olecule but also induce acid-promoted reactions. [64] Theset ypes of catalysts are especially useful for oil refinery processes involving catalytic hydrocracking. [65] In these processes, low-value heavy gas oils derived from natural oil can be converted into light gases,g asoline,j et fuel or diesel oil, depending on the reactionc onditions.A tt emperatures of 350-450 8 8C and ah ydrogen pressure of 60-200 atm, the reaction can take place over the zeolite catalysts. [6] These catalytic systems were introduced in 1964 by the Union Oil Company,a st hey allowed conversion of aw ider range of high boiling-points tarting materials to more valuable and shorter hydrocarbons. [66] Ad etaileda nalysis of the IPC and CPC codesr evealed that the five most abundant classifications all describe crystalline aluminosilicate zeolites.T his is expecteda st hese comprise the typical zeolitic catalyst for hydrocracking.T he significant increase in patent activity since 2000 indicates that molecular sievec atalysts are stillw idelyu sed and are continuously being improved to develop optimal hydrocracking catalysts for the selective generation of high-value fuels.F or the petrochemical industry,s light increases in catalyst activity or selectivity can substantially increase aprocesssp rofitability because of the immense scale.D evelopment of suitable catalysts can therefore have a significant impact on the economics of the overall process.

Physical Properties
TheB 01J35 class distinguishes the physical properties of catalytic bodies that have been determinedb ya ppropriate analytical techniques.S ince all the properties described in this patent class only apply to solids, we concludet hat these are heterogeneous catalysts. Figure 10 shows that in the 1970s,t he characterization of catalysts started to follow am ore strictly scientific approach. [30] This could imply that more and more effortwas devoted to the analysisand the understanding of structure-activity relationships in heterogeneous catalysts,t hus moving away from a" black-box" perception of heterogeneous catalysts. [67] Based on the more detailedC PC codes,t he B01J35 class allows ad etailed viewo ft he properties of patented catalysts in heterogeneous hydrogenation. It can be assumedt hat the distribution of the properties, as seen in the patent data, can giveapicture of the actualp roperties of catalysts applied in chemical processes.F igure 11 shows that certain properties occur more often than others.T he properties are specific surface area, average pore volume and average pore diameter, andt hey are important for the catalystss electivity,a ctivity,a nd recyclability.M oreover, these geometric properties are related and therefore interdependent on each other.
Thes pecifics urface area of catalysts of 100-500 m 2 g À1 is the most common category found in the evaluated patents (55% of the patents classified in this section). In principle,t he catalyst specific surface should correlate with the speed of the catalyzed reaction as the reactionmixture is in contact with ahigher fraction of the catalytic bodyp er unit. However, the specifics urface area cannot be extended without influencing other geometric parameters.I ts eemst hat  [Blue:s urface area;o range: pore volume (ml g À1 ); grey:p ore volume (nm);g reen:p ore distribution]. the surface area of catalysts of 100-500 m 2 g À1 represents an optimum, when considering the other parameters.
In heterogeneous catalysis,t he pore volumes substantially influence the kinetics of the catalyzed reaction. Here,researchers face atrade-off between favorable catalyst properties when decidingw hich pore size to use.Onthe one hand, alarge pore size is desirable because it enables sufficient mass transport inside the catalyst, so that the catalytic sites can be providedw ith enoughs tarting material and the products are released into the solutiona tasufficient speed.F urthermore,l argep ores prevent the channels in the catalyst from blocking ande ventual deactivation. On the other hand, having large poress tands in conflict with providing ah igh number of catalytic sites per unit volume (i.e., ah igh surface area) and makes the catalyst less resistant to physical impact due to its high porosity.T he pore diameter of ac atalytically active body can also be usedt oi ntroduce selectivity.F or example,acatalyst with small pores allowss mall molecules to enter, while excluding larger ones. [68,69] Fort he classification of pore sizes,d ifferent scales have been developed. Thet wo most commonly used classifications for pore volumes are 0.5-1.0 mL g À1 (47%) and < 0.5 mL g À1 (37%).

Regeneration of Catalysts
IPC class B01J38 describes processesfor catalyst reactivationa nd regeneration. During the catalytic process,c atalysts mayl ose theira ctivity due to various reasons. Major causes for the loss of activity include poisoning,f ouling, thermald egradation, mechanical damage,a nd corrosion/leaching. These processes are further described in Table 3. [71] Catalysts often contain highly precious elements like noble metals or may be difficult to prepare.T his makes catalyst regeneration an economic imperative and it is therefore desirable to maximize the lifetime of ag iven catalytic body. Despite the economic relevance of catalyst regeneration, patentinga ctivities in this domain are relatively low,a ss hown in Figure 11. Only from around 1990w as as light increase in patenting activity observed. Ap ossible explanation is that catalyst preparation and process control are considered to be the major sources of competitive ad-vantage,w hile catalyst regeneration is not as critical and therefore less patented.
We believe that this abundancy is correlated with the fact that catalyst preparation ando peration is a much more valuable process knowledge to be protected by the respective company.Ap rocess for catalyst regeneration couldt hen be deriveda fter catalyst development and be kept confidential without warranting the resourcesfor the filing of arelated patent.

Results of Keyword-Based Search
In addition to using the predefined IPC and CPC classifications,w ec omplement our analysisw ith ak eyword-based approach. In so doing, developments in hydrogenation catalysis that are not captured by the abovec lassifications are illuminated. Figure 12 shows Table 3. Five main reasons for the loss of catalytic activity. [62] Cause of activityloss

Poisoning
Strong adsorption of impurities in the reaction mixture chemically blockingt he active sites Fouling Solid deposition on the catalysts surface physically blocking the active sites Thermal degradation Sintering, evaporation or diffusioni nto an inert support of catalytically active chemical entities reducing the amountofc atalytically active surface Mechanical damage Disintegration of catalytically active entities by mechanical stress,destruction of structure and lossofc atalytically active sites Corrosion/ Leaching Dissolution of active sites or the structure of acatalyst support, loss of active sites and structure Figure12. Results of keyword-based search for selected hydrogenation reaction types. the patent grantsf or enantioselective hydrogenation, transfer hydrogenation, hydrodeoxygenation, and the use of nanoparticles from 1970-2017.A st his figure shows,t he economic interest in enantioselective hydrogenation, after peaking two years after the Nobel prize was rewarded to Noyori in 2001, continues to be at as ubstantial level. Innovations in transfer hydrogenation are being continuously patented at ar ateo f around 50 grants per year. Furthermore,n anoparticles are findingi ncreasing use for catalyzed hydrogenation reactions.P atent grantsi nt his relatively young field have seen as ignificant increase since around the year 2010, indicating its emerging industrial relevance.P erhaps most noteworthy,t he current number of patent grants in field of hydrodeoxygenation (HDO) surpasses all others.H DO describes as eries of reactions that aim at converting biomass-derived substrates into renewablef uels and chemicals. [72] Theu rge to fightc limate change accelerates the development of this technology at industriallyr elevant scales.A nanalysis of metal-organic frameworks (MOFs) was also done, but industrial applications are still in their infancy,r esearch is mainly driven by universities,a nd therefore overallp atents are scarce.I nt erms of the technology life cycle,MOFs are an emerging technology.

5C onclusions
This review presents an overview of the patent landscape of hydrogenation catalysts.
Among the different catalyst types,a ctive metal components andc atalyst support have the highest competitive impact,b ut molecular sieve-based catalysts are characterized by an increasing competitive impact in recent years,e xceeding catalysts based on coordination complexes and hydrides.O nb reaking down patent activity of different ligand structures of homogeneous hydrogenation catalysts,p hosphoruscontainingl igands constitute the majority of applied complexes,f ollowed by ligands containing nitrogen and unsaturated compounds. Within the group of heterogeneous hydrogenation catalysts,p alladium is found to be the most prevalent metal component, while rhodium is most frequently used among homogeneoush ydrogenation catalysts.H owever, the patent analysis revealed for both heterogeneous andh omogeneoush ydrogenation that other metal components are showing ah igher patent activity in recent years, mainly driven by patentinga ctivitiesi nC hina. Ag eographical analysis revealed that Chinah as ar elatively strong focuso nh eterogeneous catalysts anda bundant metals like nickel or iron. Furthermore,a ni ncreasing R&D efforti sd evoted to the physical properties of solids.
While the classification-based search was useful to differentiate between different technologies in hydro-genation catalysis,c omplementing the results with an informed keyword-baseda pproach is worthwhile.H ydrodeoxygenation stood out in this analysis,s howing ar apidly increasing bodyo fp atents granted pery ear.
Accordingt ot he technologicall ife cycle concept, hydrogenation catalysis can be consideredt ob ei ni ts growths tage,a si ndicated by high market penetration and simultaneously accelerating patentinga ctivities. Then umber of patent familiesi nh eterogeneous hydrogenation grows twice as fast as the number of patent familiesi nh omogeneoush ydrogenation,w hich is in accordance with its industrial applicability.F inally,c atalysisw hose purpose alignsw ith contemporary societalc hallenges,s uch as climate change,w illf eature above average growth rates in patents.