Chemistries mediating deactivation in methanol to hydrocarbons conversion and strategies to mitigate them

The conversion of methanol-to-hydrocarbons represents the final step in upgrading carbon feedstocks, such as coal and shale gas, to high-value fuels and chemicals. The shape selective characteristics of zeolites afford high selectivity to light olefins or gasoline-range hydrocarbons, but are deleterious for catalyst lifetime, as the accumulation of bulky hydrocarbons inside micropores renders them inactive. The goals of this research are to explore mechanisms involved in forming these inactive occluded hydrocarbon species, and to develop formulations and process conditions to improve catalyst lifetime and selectivity. The research will help ensure efficient utilization of the Nation's fossil fuel resources by the energy and chemical industries.

Methanol-to-hydrocarbons conversion proceeds auto-catalytically with olefins- and aromatics-based intermediates localized inside the zeolite pores, constituting the so-called 'hydrocarbon pool,' acting as organic co-catalysts for carbon-carbon bond formation events. This research seeks to examine the pathways that mediate the conversion of active hydrocarbon pool intermediates to inactive polycyclic hydrocarbons. It is predicated upon preliminary results that suggest methanol acts as a hydride donor during catalysis and derivatives of methanol dehydrogenation act as alkylation agents effecting hydrocarbon pool deactivation. The project is aimed at determining the rate and mechanism by which methanol dehydrogenation events occur using isotopic methods combined with transient and steady state kinetic measurements. The researchers propose that catalyst lifetime can be improved by (i) modifying the inorganic catalyst by introducing spatial constraints to mitigate formation of bulky hydrocarbons or by addition of metal oxides that decompose aldehydes, and (ii) introducing an organic co-catalyst prior to introduction of methanol containing streams in the vapor phase. The researchers expect that the strategies developed in this research for proton-form MFI and CHA zeolites will extend to other zeolite topologies and will inspire the design of materials for applications in heterogeneous catalysis extending beyond methanol-to-hydrocarbons catalysis. In addition to providing opportunities for undergraduate and graduate student training, the principal investigator will pursue educational and outreach programs that introduce concepts of catalysis across the K-12 curriculum.