A Quantitative Multi-Scale Analysis for Revealing Site-Proximity Effects in Tandem Catalysis

Tandem conversions underpin both conventional and emerging processes, from alkane isomerization to CO2 upgrading to fuels. These conversions are often treated as sequential reactions and guided by the qualitative proximity-criterion “the closer the better”, overlooking how reaction networks, thermodynamics, and transport govern site-proximity effects. Herein, we investigate their origins for CH3OH-mediated CO2 hydrogenation over oxide/zeolite catalysts by analyzing reaction pathways, thermodynamics, and transport processes across length-scales. We reveal molecular-scale nuances that influence overall rates and selectivity. Specifically, CH3OH decomposition to CO on redox sites feeds the hydrocarbon-pool mechanism on zeolite acid sites through Koch-type carbonylation, tuning aromatic selectivity. To elucidate how transport dictates rates at reactor-scale, we propose a transport-resistance model quantifying intrapellet and zeolite intrapore diffusion at different proximities. Finally, we link transport effects to process-level metrics (e.g., net profit and CO2 emissions), elevating the proximity-criterion to a quantitative basis for rational catalyst design and benchmarking of tandem conversions.