Pyridine adsorption and reaction on Mo(1 1 0) and C/N–Mo(1 1 0): experiment and modeling

Abstract

The adsorption of pyridine (C 5H 5N) on clean and carbon/nitrogen-modified Mo(1 1 0) surfaces has been investigated using temperature-programmed desorption (TPD) and density-functional theory (DFT) calculations. Pyridine adsorbs and decomposes on Mo(1 1 0) and C/N–Mo(1 1 0) at temperatures less than 530 K. Molecular pyridine desorption on clean Mo(1 1 0) occurs at temperatures of 375 ± 5 K ( E ads = 23.5 ± 0.3 kcal mol −1) and 530 ± 5 K ( E ads = 33.6 ± 0.3 kcal mol −1). At higher exposures, a multilayer physisorption peak was also observed at ≈260 K ( E ads = 10.4 ± 0.3 kcal mol −1). Pyridine decomposition on Mo(1 1 0) results in surface carbon and nitrogen accumulation, and gaseous dihydrogen. The energetics of various pyridine adsorption modes were calculated with DFT in order to identify the bonding modes resulting in molecular desorption and surface decomposition. The DFT calculations suggest that pyridine initially adsorbs as η 6-Py-0° coordination followed by η 1(N)-Py-90° adsorption on clean Mo(1 1 0), and surface heating is suggested to result in the transformation of a portion of η 6-Py-0° pyridine to surface α-pyridyl species (μ 2,η 2(N,C2)-Pyridyl, η 2(N,C2)-Pyridyl) that further decompose to surface carbon and nitrogen and desorbing dihydrogen on clean Mo(1 1 0).