Liquid and gas-phase Meerwein–Ponndorf–Verley reduction of crotonaldehyde on ZrO2 catalysts modified with Al2O3, Ga2O3 and In2O3

A series of catalysts consisting of ZrO2 modified with Al, Ga and In by coprecipitation with their precursor salts or impregnation of previously synthesized ZrO2 with the nitrates of the metals was prepared. The solids thus obtained were characterized using a wide range or techniques including TG/DTG; XRD, SEM-EDAX, ICP-MS, FTIR and FT-Raman spectroscopies; and nitrogen adsorption–desorption at 77 K. The catalysts prepared by impregnation were found to contain Al, Ga and In nitrates while those obtained by coprecipitation contained Al2O3, Ga2O3 and In2O3. The catalysts were analyzed for surface acidity and basicity by thermal programmed desorption of pyridine and CO2, respectively. The impregnated solids calcined at 300 °C exhibited low basicity and moderate acidity due to Brønsted and Lewis sites. The coprecipitated solids were slightly more acid and basic than their impregnated counterparts, their acidity being mainly due to the presence of Brønsted sites. Both types of solids were used as catalysts in the Meerwein–Ponndorf–Verley reduction of crotonaldehyde with 2-propanol as hydrogen donor. The impregnated solids calcined at 300 °C (particularly the Ga/ZrO2 catalyst) were the most active and selective ones in the liquid phase reaction. The selectivity towards 2-butenol in the reaction in the gas phase was high at temperatures up to 250 °C, above which it dropped in a rapid manner. Again, the impregnated solids calcined at 300 °C were the most active and selective systems in the process (particularly Ga/ZrO2).

Graphical abstractA series of catalysts consisting of ZrO2 modified with Al, Ga and In were synthesized by coprecipitation and impregnation methods. The impregnated solids exhibited low basicity and moderate acidity (Brønsted + Lewis). The coprecipitated ones were slightly more acid (Brønsted) and basic than their impregnated counterparts. The impregnated solids (particularly the Ga/ZrO2 catalyst) were the most active and selective ones towards 2-butenol in Meerwein–Ponndorf–Verley reduction of crotonaldehyde.Figure optionsDownload full-size imageDownload high-quality image (101 K)Download as PowerPoint slideResearch highlights► Al, Ga or In impregnated ZrO2 catalysts showed Lewis acidity. ► Coprecipitated counterparts are more basic and Lewis component is lacking. ► Impregnated catalysts were the most active in selective crotonaldehyde reduction ► High selectivity (80–88%) to crotyl alcohol was found for all catalysts at 200 °C.