Fourier transform infrared study of butene adsorption and reaction on a silica-supported nickel catalyst

Abstract

The adsorption of 1-butene, trans-2-butene, cis-2-butene, and 1,1- d 2-1-butene on a well-characterized silica-supported nickel catalyst was studied using Fourier transform infrared spectroscopy. The resultant hydrocarbon surface species were subjected to vacuum and hydrogen. Reaction products were monitored at temperatures from 28 to 100 °C. The initial adsorption of each of the n-butenes resulted in similar infrared spectra. The main spectral features are proposed to be associated with two surface species: a weakly adsorbed 2,3-dimetallabutane and a strongly adsorbed 1,1,2- and/or 1,1,3-trimetallabutane. The surface orientations of the initially adsorbed metallabutanes are discussed along with the effect of the surface selection rule on the observed infrared bands. Heating the catalyst under vacuum resulted in the desorption of the 2,3-species to form butane and the further dehydrogenation of other metallabutanes. The addition of hydrogen to the initially adsorbed surface species resulted in the evolution of butane and the partial hydrogenation of the strongly adsorbed metallabutanes. The resultant structures were relatively stable in hydrogen at temperatures to 120 °C. Evidence was also found for the presence of allylic species during the linear isomerization of the n-butenes. It is proposed that allylic species may be precursors to the formation of the metallabutanes as well as possible intermediates in the isomerization reaction.