Synthesis of higher alcohols on copper catalysts supported on alkali-promoted basic oxides

Abstract

K±Cu y Mg 5 CeO x and Cs±Cu/ZnO/Al 2 O 3 are selective catalysts for the synthesis of alcohols from an H 2 /CO mixture at relatively low pressures and temperatures. CO 2 produced in higher alcohol synthesis and water±gas shift (WGS) reactions reversibly inhibits the formation of methanol and higher alcohols by increasing oxygen coverages on Cu surfaces and by titrating basic sites required for aldol-type chain growth steps. Inhibition effects are weaker on catalysts with high Cu-site densities. On these catalysts, the abundance of Cu sites allows reactants to reach methanol synthesis equilibrium and maintain a suf®cient number of Cu surface atoms for bifunctional condensation steps, even in the presence of CO 2 . The addition of Pd to K±Cu 0.5 Mg 5 CeO x weakens CO 2 inhibition effects, because Pd remains metallic and retains its hydrogenation activity during CO hydrogenation. Basic sites on Mg 5 CeO x are stronger than on ZnO/Al 2 O 3 and they are more ef®ciently covered by CO 2 during alcohol synthesis. K and Cs block acid sites that form dimethylether and hydrocarbons. Alcohol addition studies show that chain growth occurs predominantly by aldol-type addition of methanol-derived C 1 species to ethanol and higher alcohols, following the rules of base-catalyzed aldol condensations. The initial C±C bond formation required for ethanol synthesis, however, proceeds directly from CO, at least on K±Cu y Mg 5 CeO x catalysts. A detailed kinetic analysis shows that chain growth probabilities are very similar on K±Cu y Mg 5 CeO x and Cs±Cu/ZnO/Al 2 O 3 catalysts. The growth probabilities of C 1 chains to ethanol and of iso-C 4 chains to higher alcohols are much lower than for other chain growth steps. # 1998 Elsevier Science B.V.

Isobutanol-Methanol Mixtures From Synthesis Gas

“…This indicates that one pathway for ethanol to 1-propanol chain growth involves carbonylation of C 2 H 5 OH by 13 CO. This is consistent with linear chain growth pathways that lead to the formation of some 1-butanol during CO hydrogenation on Cs-CuZnAlO x [56].…”

“…This result indicates the importance of Cu in ethanol dehydrogenation. Moreover, CO 2 has a weaker effect on copper activity than on MgO activity [56]. Again, the main product was acetaldehyde, with small amounts of acetone, ethyl acetate, n-butyraldehyde, and β-ketobutanal (Figure 2.27b …”

“…MG3-11 O/K was re-washed and reimpregnated to give MG3-11 Ow/K (0.9 wt% K-Cu 0.5 Mg 5 CeO x ); the latter gave a surface area of 145 m 2 /g, suggesting that the efficiency of K removal during synthesis is the cause of the observed variation in BET surface area and Cu dispersion. While unpromoted catalysts, Cu-Mg-Ce system (Catalysts MG3-1bO, MG3-11O, and MG3-10 O) showed similar surface areas (108, 93, and 96 m 2 /g), the K-impregnated oxides (Catalysts MG3-1bO/K, MG3-11 O/K, and MG3-10 O/K) showed significantly different surface areas (89,56, and 190 m 2 /g). It suggests that K-impregnation is critical in the control of surface area (Table 1.3).…”

“…Also, in the high-pressure methanol and isobutanol synthesis from CO/H 2 on K-promoted CuMgCeO x [30,56]. In order to examine the effects of CO 2 on both ethanol dehydrogenation and coupling reactions, reaction rates were measured on 1.0 wt % K-Cu 0.5 Mg 5 CeO x and 1.2 wt % K-Cu 7.5 Mg 5 CeO x catalysts by adding CO 2 (3.5 kPa, 20 kPa) to ethanol/H 2 (4.0/29.3 kPa) reactant mixtures at 573 K.…”

Methanol to Long-chain Oxygenates Over Mg/Al Mixed Oxides Supported Cu Catalysts

“…When Cu catalysts are modified by base additives such as Na, K, Cs, and Zr [22][23][24][25][26][27][28], higher alcohols are formed and the process is known as the higher-alcohol synthesis (HAS) [29]. Products of HAS from syn-gas typically contains CO 2 , methanol, higher (C 2+ ) oxygenates (e.g., DME, MF, and higher alcohols), and some hydrocarbons.…”