Gold supported on Ti incorporated MCM-36 as efficient catalysts in propylene epoxidation with H2 and O2

Abstract

Novel catalysts consisting of gold nanoparticles (NPs) supported on the titanosilicate pillared MCM-36 (Si/Ti-MCM-36) with 2 nm mesopores were prepared. The influences of the Ti coordination environment on the particle size of the anchored Au NPs and their catalytic performances in propylene epoxidation with mixtures of H₂ and O₂ were investigated. The catalyst materials were characterized with Electron Probe Micro Analysis, X-ray diffraction, nitrogen sorption, UV-visible diffuse reflectance spectroscopy, transmission electron microscopy, and X-ray absorption spectroscopy. The coordination environment of Ti(IV) in Si/Ti-MCM-36 was found to be a mixture of octahedral (O_h) and tetrahedral (T_d). The Au loading was proportional to the amount of Ti incorporated in the porous silica. The higher loading of Ti in Si/Ti-MCM-36 anchored more Au and resulted in the formation of larger Au particles. The deposition–precipitation (DP) with NH₃ as a DP agent seemed to give Au NPs larger than those loaded by NaOH. The most efficient Au NPs size was about 1 nm, and Au NPs with sizes larger than 2 nm were not efficient for the propylene epoxide (PO) formation. By adjusting the Au and Ti synergy, the optimal PO formation rate over Au loaded Si/Ti-MCM-36 was 28.9 g_PO h⁻¹ g_cat⁻¹.