Hierarchical Ga-MFI Catalysts for Propane Dehydrogenation

Abstract

We report the synthesis, characterization, and enhanced propane dehydrogenation properties of hierarchical Ga-MFI zeolite catalysts synthesized by two different methods: (i) repetitive branching and (ii) utilization of a long chain alkyl SDA. Structural, compositional, and morphological characterizations confirm that the Ga-MFI catalyst materials have hierarchical structures including micropores and mesopores in a single particle and show that Si/Ga ratios comparable to bulk Ga-MFI catalysts can be obtained. Acid site analysis using NH 3 -TPD and pyridine adsorption followed by in situ IR spectroscopy allowed quantification of the number and types of acid sites present and show that the hierarchical catalysts have considerably higher Lewis acid site concentrations than the bulk catalysts. The hierarchical Ga-MFI catalysts show superior PDH performance (at 600 °C) compared to bulk Ga-MFI catalysts. Propane conversion rates are increased 2−6-fold and propylene selectivities are 10−100% higher. We also examine the effects of synthesis variationssuch as addition of 3-mercaptopropyltrimethoxysilane during synthesis and H + ion-exchangeand find that both these steps have a beneficial effect on PDH properties. Calculations suggest that PDH in both the bulk and the hierarchical Ga-MFI is not diffusion-limited. Therefore, the superior performance of hierarchical Ga-MFI is due to intrinsically higher activity and selectivity. Potential reasons for this behavior are outlined. The present findings showing enhancement of PDH in hierarchical Ga-MFI catalysts suggests that the utility of the hierarchical zeolites is not limited to diffusion-limited reactions involving large, bulky molecules and that they may be useful in more diverse applications involving gas-phase reactions with small molecules.

Recent Advances on Gallium-Modified ZSM-5 for Conversion of Light Hydrocarbons

“…The synthesis of Ga-modified ZSM-5 with hydrothermal crystallization has been reported [ 46 , 54 , 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 ]. Awate et al reported synthesis of Ga-modified ZSM-5 from sodium gallosilicate gel using triethyl-n-butylammonium bromide as the structure-directing agents (SDA) [ 65 ].…”

A Comprehensive Review of the Applications of Hierarchical Zeolite Nanosheets and Nanoparticle Assemblies in Light Olefin Production

“…The hierarchical Ga-MFI catalysts have a higher Lewis acid site with respect to conventional Ga-MFI. For this reason, the hierarchical Ga-MFI catalysts exhibit improved propylene selectivity from 35% to 80% at 600 • C. The higher performance relates to a lower propylene adsorption and the Brønsted and Lewis acid sites distribution around the mesopores [73]. In addition, the Pt silicalite-1 nanosheets exhibit high propylene selectivity around 95% because they can prohibit the side reaction and reduce the diffusion limitation.…”

Recent Progress in Commercial and Novel Catalysts for Catalytic Dehydrogenation of Light Alkanes

“…Therefore, the development of novel dehydrogenation catalysts is still needed. In recent years, metal oxide‐based catalysts (VO x , MoO x , GaO x , In−Ga−O, Zn−Nb−O), carbon‐based catalysts, metal sulfide‐based catalysts, Sn‐based catalysts and single atom catalysts have been extensively studied. The dehydrogenation performances of these catalysts are summarized in Table .…”