III International Conference

2-ResultsPP-I-25The present work deals with the influence of the pressure on the kinetics of the CO 2 /H 2reaction on a co-precipitated CuO/ZnO/Al 2 O 3 catalyst at 230 °C and total pressure from 1 barto 75 bars. The method of investigation is the variation of the relative selectivityγ = [CH 3 OH]/ [CO] as a function of the contact time 1/d. When the CO 2 /H 2 mixture was fedover the catalyst, methanol was produced together with carbon monoxide and water. Theobtained results show a great influence of the pressure on the reaction mechanisms. Twodomains of pressure are pointed out:i) Up to 28 bar, γ increases sharply as 1/d tends towards zero whereas 1/γ tends towards zero.This implies a reaction mechanism of the type represented in scheme III.ii) From 35 bar, γ tends towards a finite value as 1/d tends towards zero whereas 1/γ tendstowards a finite value also. Thus it appears that carbon dioxide is the immediate precursor ofmethanol in the CO 2 /H 2 reaction whatever the working pressure. The product is probablyformed, as generally accepted (1, 6), through a set of adsorbed species as following:CO 2 CO 2 ads CO 3 ads HCOOads CH 3 Oads CH 3 OHOn the other hand, carbon monoxide formation path depends on the reaction pressure. Atlow pressure it seems to stem from the decomposition of methanol re-adsorbed as a methoxyspecies on a different site:CO 2 CH 3 OHads COads CO3-ConclusionOur results show the great influence of the operating pressure on the kinetics of the CO 2 /H 2reaction on CuO/ZnO/Al 2 O 3 catalysts. Methanol is produced directly from CO 2 whatever thepressure whereas carbon monoxide stems either from decomposition of methanol at low pressureor from CO 2 directly at high pressure. The method of preparation has no influence on the reactionmechanisms, nor does the copper content of the studied solids.References:1 K.C. Waugh, Catal. Today 15(1992)512 J.C.J. Bart and R.P.A. Sneeden, Catal. Today 2(1987) 13 K. KLIER, Adv. Catal. 31(1982)2434 G.C. Chinchen, K.C. Waugh and D.A. Whan, Appl. Catal. 25(1986)101 Kinet. Catal.16(1975)7065 R. Bardet, J. Thivolle-Cazat and Y. Trambouze, J. Chim. Phys. 78(1981)13516 B. Denise, O. Cherifi, M.M. Bettahar and R.P.A. Sneeden, Appl. Catal. 48(1989)3657 H. Baussart, R. Delobel, M. Lebras, D.Le Maguer and J.M. Leroy, Appl. Catal.14(1985)38153