Effects of Support on the Formation and Activity of Gold Catalysts for Ethanol Conversion to Butanol

Using a combination of physicochemical methods, such as TEM, SEM, EDS, XPS, NH 3 –TPD, and N 2 adsorption, the study investigates the structure of a number of supports (Al 2 O 3 , SiO 2 , TiO 2 , ZrO 2 , and C) and of Au/support catalyst samples (Au = 0.5%). The concentration of highly active 2–4 nm gold particles in Au catalysts is influenced by the support’s texture; this concentration increases in the following order: Au/TiO 2 < Au/ZrO 2 < Au/C < Au/SiO 2 << Au/Al 2 O 3 . The acidity of Au catalysts is influenced by the support’s nature; this acidity decreases in the following order: Al 2 O 3 > TiO 2 > ZrO 2 > SiO 2 >> Au/C. At 275°C, a carbon support is inactive in ethanol conversion to butanol. In the presence of oxide supports, the target reaction occurs at a relatively low rate by a bimolecular condensation mechanism. Over Au/Al 2 O 3 , Au/SiO 2 , Au/TiO 2 , or Au/ZrO 2, the reaction occurs more rapidly by an aldol condensation mechanism. At an ethanol conversion of 14–18%, the butanol selectivity increases in the following order: Au/C(0) << Au/SiO 2 (0.4%) < Au/ZrO 2 (1.5%) < Au/TiO 2 (2%) << Au/Al 2 O 3 (78%). The high efficiency of Au/Al 2 O 3 stems from the high density of the Al n + –O 2– sites located on the support’s surface, and of the coordination-unsaturated Au 0 (KH) atoms located on the surface of 2–4 nm gold particles.