ChemCatChem

The cover picture shows a proposed reaction mechanism for the reduction of nitrogen oxides with CO over a silica-supported chromia catalyst. In their Communication on page 259 ff., Groppo et al. demonstrate the potential of single Cr^II active sites in this reaction. The use of FTIR spectroscopy allows identification of the intermediate species and also shows that the mechanism, incorporating three coupled catalytic cycles, depends on the NO/CO reactant ratio.

The rhodium-catalyzed hydroformylation of 3,3-dimethyl-1-butene is monitored by in situ, high-pressure FTIR spectroscopy, as pictured, giving time-dependent concentration profiles of organic components and metal–organic reaction intermediates. In their paper on page 287 ff., Selent et al. offer an improved perception of mono- and diphosphite-modified catalysis.

A perfect couple: A catalytic system for the Suzuki–Miyaura coupling has been developed, which simplifies the application of the reaction to biologically relevant compounds such as proteins in aqueous media at low temperatures.

Compulsive layers: Lamellar zeolites are crystalline layered materials with porosity within the layers. A recent breakthrough regarding the synthesis of a new lamellar zeolite with the well-known ZSM-5 structure is highlighted in light of previous work on lamellar zeolites and the emerging applications of hierarchical zeolites and zeolitic layers, which include heterogeneous catalysis and zeolite membranes.

In a future chemical industry based on biorenewable resources, new chemical transformation routes are required to convert this class of materials into new chemical building blocks. Considerations on combining heterogeneous chemoenzymatic systems are given with special emphasis on oxidase systems with the unique ability to produce and use hydrogen peroxide in situ.

Wherefore art thou, Chromia? Owing to the redox chemistry of Cr^II and the high coordinative unsaturation of the metal cation forming the active site, silica-supported chromia acts as a single-site catalyst for the reduction of nitrogen oxides by CO. The mechanism is elucidated by surface FTIR spectroscopy, which also allows characterization of the intermediate species involved in three coupled catalytic cycles.

A matter of fitness: An Arabidopsis thaliana nitrilase 2 (NIT2) variant with improved specific activity is generated by error prone PCR followed by recombination of advantageous mutations. The improvement is shown not only for the test substrate phenylacetonitrile but also for a diverse set of aromatic nitriles, dicyanides, and other functionalized nitriles.

Propene hydrogenation over cubic Pt nanoparticles (NPs) is carried out to evaluate their catalytic performance. The value of the activation energy is found to be 9.7±0.5 kcal mol⁻¹, which is discussed by comparing it to those of encapsulated and truncated octahedral Pt NPs deposited on alumina.

Operando spectroscopy: A setup is presented that enables simultaneous in situ ATR-FTIR, UV/Vis, and Raman spectroscopic measurements by implementation of spectroscopic immersion probes into a modified autoclave reactor. This setup allows the monitoring of liquid-phase hydrogenation reactions under elevated H₂ pressures.

OH, what a catalyst! Gold oxide nanoparticles grown on natural and hydroxylated TiO₂ were investigated for CO oxidation. Although clusters were grown with similar sizes, their activities differed by a factor of at least 180, depending on the degree of hydroxylation. Hydroxy groups are coincidentally introduced during the solution-phase synthesis of the catalysts and are critical for activity.

Reaction progress fully monitored: During Rh-catalyzed hydroformylation, the olefin concentration determines the ratio of monophosphite hydride and acyl intermediates detected simultaneously. Saturation kinetics are observed for the first time using a diphosphite. Within this regime, the bidentate ligand induces a turnover frequency of 1040 h^-1 compared to 237 h^-1 for the monophosphite, at 30 °C.

The palladium-catalyzed direct arylation of heterocycles with deactivated bromoarenes is promoted by ferrocenyl polyphosphanes. Among five candidates, a triphosphane is the most effective for the CH activation and CC coupling. Its coordination behavior towards group 10 metals shows an unprecedented combination of cis chelating and bis-trans-monodentate bonding.

ROP ′til you drop: The “immortal” ring-opening polymerization of trimethylene carbonate, using a two-component catalyst system based on a metal triflate and an alcohol as co-initiator and chain-transfer agent, proceeds in bulk with high activities (TOF up to 28 200 h⁻¹) and productivities (TON up to 45 000). Due to the water-tolerance of these systems, experimental operating conditions do not require any special care.

An underestimated impact: Hydrotalcites containing different organic interlayer anions have been synthesized and the derived mixed oxides applied as catalysts in the transesterification of glycerol trioctanoate with methanol to octanoic acid methyl ester. Large differences in the obtained methyl ester yields revealed a great impact of the precursor anions on catalytic activity of hydrotalcite-derived mixed oxides.

On HMS's secret surface: SBA-15 hexagonal mesoporous silica (HMS) was used for the immobilization of Pseudomonas fluorescens lipase. The chemically and physically immobilized enzymes were successfully used for biocatalytic production of biodiesel, leading to almost full conversion of sunflower oil and ethanol into the corresponding ethyl esters, and were reused for several cycles.

In good NiC: Nickel–carbon composite catalysts were synthesized by controlled carbon deposition over Raney nickel. The use of these catalysts simultaneously eliminates pyrophoricity and enhances the activity in comparison to Raney nickel. The catalysts are stable under normal atmospheric condition and exhibit excellent activity, superior to the parent Raney nickel, in the hydrogenation of several organic substrates.

Disproportionate representation: In CO disproportionation on reduced ceria, adjacent adsorbed CO molecules couple together. Upon CO bond dissociation, asymmetrical inorganic carboxylate species, the key reaction intermediates, are formed. The unpaired electrons, which are produced by reduction of the ceria surface, weaken the CO bond adsorbed onto Ce³⁺ through back- donation of electrons.

Wiley-VCH, Weinheim, 2009. 317 pp., hardcover, € 119.00.—ISBN 978-3-527-32380-7

John Wiley & Sons, Hoboken, 2009. 208 pp., hardcover, € 57.90.—ISBN 978-0-470-26101-9