The role of alumina in the supported Mo/HBeta–Al2O3 catalyst for olefin metathesis: A high-resolution solid-state NMR and electron microscopy study

High-resolution solid-state MAS NMR; hyperpolarized 129Xe NMR, SEM, and TEM; XRD; and N2 adsorption were used to investigate the role of alumina in the Mo/HBeta–Al2O3 catalyst. XRD and N2 adsorption showed that introduction of alumina into the support may protect the HBeta framework from destruction. Quantitative 29Si MAS, 27Al MAS, and MQ MAS NMR spectra demonstrated that dealumination occurs preferentially at specific T-sites in the Mo/HBeta catalyst; however, the framework aluminum in HBeta zeolites remains at the same crystallographic sites after the addition of alumina. Hyperpolarized 129Xe NMR, HRTEM, and SEM images indicate that Mo species are readily dispersed in alumina rather than in HBeta zeolites. The preferential migration of Mo species into the alumina pores may preserve the integrity of the HBeta zeolite framework and result in the moderate distribution of Mo species and acidity in the composite support. These may be correlated with the high performance of Mo/HBeta–Al2O3 catalysts in the metathesis of ethene and butene-2 to propene.