Infrared Diffuse Reflectance Spectra of CO,H 2,C 2 H 4,and C 2 H 5 OH Adsorbed on Alumina Supported Rh.

Abstract

Infrared spectra of CO, H₂, C₂H₄, and C₂H₅OH adsorbed on rhodium supported on alumina have been obtained by a diffuse reflectance technique using a Fourier Transfor spectrometer. In the temperature range from 523K to 673K surface water or hydroxyl groups can oxidize metallic Rh particles to give Rh in a positive oxidation state as indicated by the the infrared spectrum of chemisorbed CO. Reduction in H₂ at either lower or higher temperatures produces metallic Rh particles that chemisorb CO to produce broad bands for both linear and bridge bonded CO characteristic of metallic Rh particles. Aside from chemisorbed CO, the most conspicuous surface species formed during CO hydrogenation on Rh/A1₂O₃ is a surface acetate. Ethene has two main reactions with Rh/A1₂O₃; one to produce a surface ethylidyne and the other to produce gas phase ethane. The main interactions of ethanol with the Rh/A1₂O₃ are to produce a surface acetate and to decompose to produce gas phase methane. In the presence of CO the ethene reacts with surface oxygen to give a surface acetate. In no case could a surface species be found that could be identified as an intermediate in CO hydrogenation to hydrocarbons. No surface species were found that could be assigned as CO insertion products with ethene or ethanol to give C3 molecules.