(A) study on methanol dehydrogenation on copper-containing catalysis

Abstract

The copper containing catalysts such as Cu/ZnO, Cu/$ZrO_2$, Cu/$SiO_2$ were prepared by coprecipitation method and their catalytic activities were measured at 493 K and GHSV of 3000 mL(S.T.P.)/gcat.h to investigate the support effects on methanol dehydrogenation. The reaction rate was mostly proportional to the copper surface regardless of the supports. The Cu/ZnO catalysts were the most selective among the prepared catalyts, but suffered from severe deactivation and the deactivation phenomena was dependent on the supports. It was been observed that the ZnO in the Cu/ZnO catalyst could be reduced by pulse reaction with methanol. TPR studies in H2, CO and methanol with an aid of microbalance were conducted at the temperature range from 323 K to 623 K to study the reduction of ZnO in the Cu/ZnO catalyst. It has been confirmed that methanol and CO can reduce the ZnO in the catalyst, while H2 cannot. The reduction of ZnO with methanol and CO can occurs in the presence of copper in the vicinity of ZnO. Along with the study on the reduction of bulk ZnO in the Cu/ZnO catalyst, surface composition of ZnO in the catalyst samples was analyzed with X-ray photon electron spectroscopy. The catalyst samples were prepared under different conditions: 1) calcined at 723 K for 16 h, b) reduced at 623 K for 1 h by hydrogen after the calcination, c) reacted with methanol at 523 K for 3 h after the calcination. X-ray induced Auger spectra of Zn ($L_3M_{4,5}M_{4,5}$) gave the result that 14% of ZnO on the surface of the $H_2$ reduced sample was reduced to metallic zinc after the reacion with methanol at 523 K for 3 h. The suppession of the reduction of ZnO in the catalyst was attempted by intoducing an oxidant, such as $CO_2$ or oxygen, into reactant feed. TPR of the Cu/ZnO catalyst with methanol on a enclosed microbalance was conducted in the presence of $CO_2$. Then, the reduction of ZnO in the Cu/ZnO catalyst could be effectively controlled by $CO_2$, which was well correlated wi...