Distance for Communication between Metal and Acid Sites for Syngas Conversion

Abstract

Unraveling the proximity influence between different sites in tandem catalysis is particularly challenging. Herein, we evaluate the distance effect on the communication between metal and acid sites in a methanol-mediated syngas conversion system. A series of catalysts composed of ZnZrOx and zeolites with different proximity levels from the millimeter scale to nanoscale were evaluated in the syngas to olefins (STO), gasoline (STG), and aromatics (STA) reactions. The distance requirements are dependent on the diffusivity of reaction intermediates and the formation mechanism of products. The STO and STG reactions follow a simple tandem mechanism, which is not sensitive to the distance as long as the gaseous methanol could fast diffuse to acid sites. Whereas a synergistic tandem mechanism for syngas to aromatics is evidenced, i.e., the dehydro-aromatization step must be promoted by the intimate contact of metal and acid sites to eliminate the surface hydrogen species on zeolites by recombinative hydrogen desorption.