CO HYDROGENATION TO HIGHER OXYGENATES OVER PROMOTED RHODIUM - NATURE OF THE METAL-PROMOTER INTERACTION IN RHMN NAY/

Unpromoted and manganese-promoted zeolite Y supported rhodium catalyst s were tested for CO hydrogenation at 1 MPa and 250 degrees C. The con ditions of catalyst preparation by ion exchange, programmed calcinatio n, programmed reduction and neutralization of acid sites were varied s ystematically in order to compare the promoter effects of different sp ecies of manganese. It is found that only MnO particles, and not Mn2ions, promote the Rh-catalyzed formation of the abundant oxygenates et hanol and ethyl acetate. No reduction in Mn-0 or Rh-Mn alloy formation takes place. Temperature-programmed reduction profiles of Mn/NaY and RhMn/NaY show that reduction of MnO2 to MnO is dramatically enhanced b y Rh, indicating that in the reduced catalyst Rh clusters and MnO clus ters are in physical contact. Direct interaction between Rh and MnO al so follows from EXAFS data which show that the Rh-Rh coordination numb er is much lower in NaY when MnO particles are present. TPD results in dicate that MnO affects the propensity of Rh to chemisorb hydrogen. Te ntative reaction mechanisms for CO hydrogenation are considered, consi stent with the experimental findings. (C) 1995 Academic Press, Inc.