Theoretical study of Au/SAPO-11 catalyst and its potential use in thiophene HDS

Quantum chemistry calculations were carried out, using ONIOM2 methodology, in order to investigate the thiophene interaction with gold supported on silicoaluminophospates molecular sieves (Au/SAPO-11) catalysts. Two models were studied, one containing one Au atom per site, and the other with two Au atoms per site. Thiophene adsorption was found to be η¹ type. This adsorption presents a ΔH of -13.2 and -9.7 kcal/mol, for the models with one Au atom (Au/SAPO-11), and two Au atoms (Au₂/SAPO-11), respectively. The partial hydrogenation of the thiophene-Au/SAPO-11 and thiophene-Au₂/SAPO-11 complexes gives 2,5-dihydrothiophene (DHT), with a ΔH of -23.0 and -36.8 kcal/mol, respectively. 2-Butene production was found in both models with further hydrogenation. Likewise the direct butadiene elimination is achieved, but only with the separated Au dimer (ΔH = -17.5 kcal/mol).