Zeolite-Encapsulated Ultrasmall Cu/ZnOₓ Nanoparticles for the Hydrogenation of CO₂ to Methanol

Selective hydrogenation of CO₂ to methanol is a “two birds, one stone” technology to mitigate the greenhouse effect and solve the energy demand–supply deficit. Cu-based catalysts can effectively catalyze this reaction but suffer from low catalytic stability caused by the sintering of Cu species. Here, we report a series of zeolite-fixed catalysts Cu/ZnOₓ(Y)@Na-ZSM-5 (Y is the mass ratios of Cu/Zn in the catalysts) with core–shell structures to overcome this issue and strengthen the transformation. Fascinatingly, in this work, we first employed bimetallic metal–organic framework, CuZn-HKUST-1, nanoparticles (NPs) as a sacrificial agent to introduce ultrasmall Cu/ZnOₓ NPs (∼2 nm) into the crystalline particles of the Na-ZSM-5 zeolite via a hydrothermal synthesis method. The catalytic results showed that the optimized zeolite-encapsulated Cu/ZnOₓ(1.38)@Na-ZSM-5 catalyst exhibited the space time yield of methanol (STYMₑOH) of 44.88 gMₑOH·gCᵤ–¹·h–¹, much more efficient than the supported Cu/ZnOₓ/Na-ZSM-5 catalyst (13.32 gMₑOH·gCᵤ–¹·h–¹) and industrial Cu/ZnO/Al₂O₃ catalyst (8.46 gMₑOH·gCᵤ–¹·h–¹) under identical conditions. Multiple studies demonstrated that the confinement in the zeolite formwork affords an intimate surrounding for the active phase to create synergies and avoid the separation of Cu–ZnOₓ interfaces, which results in an improved performance. More importantly, in the long-term test, the Cu/ZnOₓ(1.38)@Na-ZSM-5 catalyst exhibited constant STYMₑOH with superior durability benefitted from its fixed structure. The current findings demonstrate the importance of confinement effects in designing highly efficient and stable methanol synthesis catalysts.