Effect of Sn addition to Pt/CeO2–Al2O3 and Pt/Al2O3 catalysts: An XPS, 119Sn Mössbauer and microcalorimetry study

The effect of adding Sn to Pt/CeO2–Al2O3 and Pt/Al2O3 catalysts was studied with X-ray photoelectron spectroscopy (XPS), 119Sn Mössbauer spectroscopy, and adsorption microcalorimetry of CO at room temperature. Catalysts were reduced in situ at 473 (non-SMSI state) and 773 K (SMSI state). 119Sn Mössbauer and XPS results indicated that the presence of cerium in bimetallic catalysts inhibited reduction of tin, and that tin facilitated the reduction of cerium(IV) to cerium(III). Microcalorimetric analysis indicated that adding cerium caused the appearance of a more heterogeneous distribution of active sites, whereas adding tin led to a higher homogeneity of these sites. Reduction at 773 K decreased the Pt surface area as measured by CO chemisorption for all catalysts used in this study. Adding tin to Pt/Al2O3 and Pt/CeO2–Al2O3 also decreased the Pt surface area due to formation of PtSn and possibly Pt–SnOx species. Adding cerium to Pt/Al2O3 caused a loss of Pt surface area only when the catalyst was reduced at 773 K, presumably due to migration of the reduced cerium onto Pt particles. Adding cerium to Pt/Al2O3 caused an increase in the catalytic activity for crotonaldehyde hydrogenation, whereas adding Sn to Pt/Al2O3 decreased the activity of Pt/Al2O3 catalysts. Higher reduction temperatures caused an increase in the initial catalytic activity for crotonaldehyde hydrogenation for all catalysts studied. Selectivity enhancements for crotyl alcohol formation in crotonaldehyde hydrogenation were observed for the Ce- and Sn-promoted catalysts after reduction at 773 K.Financial support by the Comisión Interministerial de Ciencia y Tecnología (Projects BQU 2000-0467 and BQU 2003-06150) is gratefully acknowledged