Development of hierarchical zeolites with enhanced mass transport for bulky chemical conversion

W. Fan
University of Massachusetts, Amherst,
United States

Keywords: zeolites, catalysis


Increasing demand for energy and commodity chemicals has led to accelerated research efforts in the conversion of renewable resource into chemicals and fuels for a sustainable economy. The processing of lignocellulosic biomass, an inexpensive, abundant and sustainable source of carbon, offers the promise of sustainable chemicals and carbon-neutral liquid transportation fuels. The International Energy Agency (IEA) laid out a 'roadmap' to ramp up the use of biofuels converted from biomass feedstocks from around 2% of global transport fuel at 2011 to 27% by the year 2050. Zeolite catalysts have shown superior catalytic activity and selectivity for converting lignocellulosic biomass into fuels and chemicals including aromatics and olefins because of the intrinsic ordered micropore structures and unique catalytic activity of zeolite catalysts. However, the micropore structures and high intrinsic activities frequently lead these materials to be subject to diffusion limitations that restrict reactant accessibility to the active sites on the interior surfaces of zeolites, inhibit the full utilization of zeolite catalysts, and cause fast catalyst deactivation. Synthesis of hierarchical zeolites with mesoporosity is a proven strategy for reducing the diffusion limitation in zeolite catalysts. In our group, we have developed a series of methods to synthesize hierarchical zeolites with controllable microporosity and mesoporosity, and develop zeolite catalysts for converting lignocellulosic biomass into chemicals and fuels. In this talk, I will first focus on the introduction of synthesis of hierarchical zeolites. The mass transport properties and catalytic properties of these hierarchical zeolites for biomass conversion will be discussed along with the future aspect regarding the rational development of hierarchical zeolites. In addition, we have proposed a renewable method of producing renewable p-xylene by cycloaddition of biomass-derived dimethylfuran (DMF) and ethylene, which serves as the last step in a complete process for producing p-xylene from cellulose.5 The reaction occurs by symmetry-allowed [4 + 2] Diels-Alder cycloaddition of ethylene and DMF and subsequent aromatization by acid-catalyzed dehydration to p-xylene. We recentely developed a new type of zeolite catalyst, that is, phosphorous-containing siliceous zeolites.6 The catalysts can selectively catalyze the dehydration reaction from the furan-ethylene cycloadduct to p-xylene, without catalyzing reactions producing alkylated and oligomerized products. In particular, the phosphorous-containing zeolite Beta (P-BEA) and hierarchical self-pillared pentasil, P-SPP, are active, stable and selective catalysts for this reaction with an unprecedented p-xylene yield of 97%. This catalytic behavior is distinct from that of other solid catalysts and establishes a commercially attractive process for renewable p-xylene production.