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.