The synthesis of DNL-6 with a high concentration of Si (4 Al) environments [Si/(Si+Al+P)=0.182 mol, denoted as M-DNL-6] is demonstrated. This represents the highest reported concentration of such environments in silicoaluminophosphate (SAPO) molecular sieves. Adsorption studies show that the high Si (4 Al) content in M-DNL-6, with an increased number of Brønsted acid sites in the framework, greatly promotes the adsorption of CO2. M-DNL-6 exhibits a large CO2 uptake capacity of up to 6.18 mmol g−1 at 273 K and 101 kPa, and demonstrates high ratios of CO2/CH4 and CO2/N2 separation. From breakthrough and cycling experiments, M-DNL-6 demonstrates the ability to completely separate CO2 from CH4 or N2 with a dynamic capacity of approximately 8.0 wt % before breakthrough. Importantly, the adsorbed CO2 is easily released from the adsorbent through a simple gas purging operation at room temperature to regain 95 % of the original adsorption capacity. These results suggest that M-DNL-6 can be used as a potential adsorbent for CO2 capture in pressure swing adsorption processes.