ACTIVITY AND SELECTIVITY IN CARBON-MONOXIDE HYDROGENATION OVER RHODIUM SUPPORTED ON PURE ZIRCONIA AND ON K-DOPED, P-DOPED, AND Y-DOPED ZIRCONIA

Catalysts for the CO/H2 reaction were prepared by supporting Rh4(CO)12 on pure ZrO2, with different phase compositions, and on ZrO2 doped at the surface or in the bulk with K20, P205, or Y2O3, and by decomposing the supported carbonyl in a hydrogen stream at 523 or 823 K. The catalysts were characterized by XRD, oxygen and hydrogen chemisorption, TPR, FT-IR/PAS, and catalytic activity measurements both in temperature-programmed experiments and in isothermal condition runs, at atmospheric pressure and with different feed compositions. The phase composition of the support or the doping procedure (bulk or surface) has a minor effect on the physicochemical properties and catalytic activity. Also, the various doping agents, with the exception of K20, have minor effects. K2O doping decreases the activity and changes the selectivity of Rh/ZrO2 in the CO/H2 reaction, favoring the formation of oxygenated compounds. Activation at high temperature (823 K) decreases the activity but does not change the selectivity of the catalysts. A significant influence of the feed HZ/CO ratio on activity and selectivity has been found: activity decreases with Hz/CO ratio and selectivity to oxygenates increases. The role of the various parameters investigated is discussed. © 1990.