PdZn on ZSM-5 nanoparticles for CO2 hydrogenation to dimethyl ether: comparative in situ analysis with Pd/TiO2 and PdZn/TiO2

CO2 hydrogenation to dimethyl ether was investigated on PdZn alloy deposited onto ZSM-5 nanoparticles. The effect of ZSM-5 morphology and textural properties were investigated on the efficiency of CO2 conversion and product selectivities. ZSM-5 nanoparticles showed higher conversion and selectivity towards DME than the elongated cubic ZSM-5. Uniform nanospherical ZSM-5 formed interparticle mesoporosity and improved surface area for efficient CO2 adsorption and diffusion. Comparative in situ analysis on PdZn/ZSM-5, PdZn/TiO2, Pd/TiO2 and physically mixed PdZn/TiO2 + ZSM-5 allow an understanding of the role of PdZn alloy and solid acid support in forming intermediate species during hydrogenation. CO2 was transformed into adsorbed carbonate and hydrogenated into bicarbonate and methoxy CH3O* on Pd and PdZn. However, Pd caused C-O dissociation to form methane, while PdZn stabilized CH3O* to form methanol on TiO2. Solid acid ZSM-5 catalyzed dehydration of two CH3O* to form dimethyl ether.