The roles of CO and CO2 in high pressure methanol synthesis over Cu-based catalysts

The roles of CO and CO2 in Cu-catalyzed methanol synthesis from syngas were evaluated experiments with gas switching between CO/H2 CO2/H2 feeds a CO2/CO/H2 feed corresponding CO-free CO2/inert/H2 feed. Switching CO/Ar/H2 (3/29/68) CO2/N2/H2 for Cu/Al2O3 showed that the rate on Cu is more than an order magnitude higher compared to CO. Experiments at low conversion conditions negligible product formation, purely inhibiting Raney range supported (on SiO2, TiO2, Al2O3 ZnO) Cu-catalysts including industrial-type Cu/ZnO/Al2O3 catalyst. Given generality across Cu-based samples mechanism this inhibition most likely competitive adsorption surface. However, as increased by lowering space velocity there sharp transition beneficial role relative With increasing water formed, far stronger inhibitor catalysts CO, effect arises removal through water–gas shift reaction. At thus highest minimizes inhibition, whereas high optimal CO-rich inhibition. these two types behavior occurs around leading 1 mol% effluent gas. Hence, has commercial conditions. ZnO support exerts strong, conditions, where strong reductant negative effect. This could suggest reduced Zn-sites (oxygen vacancies or Cu-Zn surface alloy sites), whose concentration are expected depend reductive potential atmosphere, not critical ZnO. both industrial (523 K, 50 bar), mild (448 atm. pressure) nominally oxidizing (498 20 bar > H2) addition detrimental activity supports plays no facilitating ZnO-reduction possibly Zn alloyed into unimportant catalytic activity.