NMR Study of the Chemisorption and Surface Chemistry of Methylamine on Pd/SiO2

Results of an investigation of the interaction of methylamine with a Pd/SiO2 catalyst utilizing nuclear magnetic resonance (NMR) spectroscopy are presented. Two sets of experiments were conducted. In one set, a sample of catalyst was initially exposed to 13CH315NH2 at 77 K and then subjected to a lengthy equilibration period at 190 K. A 13C spectrum at 77 K obtained on the sample at this point exhibited a single symmetric line at a frequency very close to the resonance frequency for methylamine in the absence of the catalyst. The line is attributed to methylamine adsorbed without dissociation. In 13C spectra obtained at 77 K on the sample after each of a series of subsequent annealing periods at successively higher temperatures in the range 253−298 K, the line exhibited a gradual broadening on the downfield side. Deconvolution of the spectra resolved the original symmetric line from a very broad downfield line attributed to partially dehydrogenated surface species designated by the formula (CN)Hx. In the ...