(509r) Tungsten Carbides As Active Catalysts for CO2 Hydrogenation | AIChE

(509r) Tungsten Carbides As Active Catalysts for CO2 Hydrogenation


Juneau, M. B. - Presenter, University of Rochester
Porosoff, M., University of Rochester
Transition metal carbides are an attractive substitute for noble metal catalysts for carbon dioxide hydrogenation due to their low cost and high selectivity to desired products (CO, CH4, or hydrocarbons). Supported Mo2C and WC exhibit high selectivity toward CO during reverse water-gas shift (RWGS),1 however WC-based catalysts show relatively lower catalytic activity due to the high synthesis temperature resulting in nanoparticle agglomeration and low availability of active surface sites. Previous work suggests the W2C phase is more active for RWGS,2 although individual carbide phases have not yet been isolated and examined for CO2 hydrogenation.

Our investigations aim to isolate the RWGS active phase of WCx-based catalysts by adjusting synthetic and carburization parameters. Nano-WCx is synthesized via an adapted micelle synthesis method3 and contrasted to an incipient wetness impregnation (IWI) control to investigate effects of particle size and carburization profiles on the tungsten phase, and in turn, RWGS performance. Based on our prior results over alkali-promoted WCx, we hypothesize that maximizing the active surface area and W2C phase will result in the highest performing catalyst. TEM images indicate a particle size of ~10 nm for the nano-WCx, in contrast to ~ 30 nm over the IWI control as shown in Figure 1. The tungsten phase is confirmed as W2C over the nano-WCx and as a mixed carbide (W2C and WC) over the IWI control via X-ray characterization techniques (XRD and XPS). Pulse chemisorption and temperature programmed desorption experiments show increased CO uptake over nano-WC suggesting a greater availability of active sites with smaller W particle size. Packed bed reactor studies illustrate nano-WCx is more active compared to the IWI control (CO space-time yields of 65.9 µmol CO/gTungsten/s and 11.8 µmol CO/gTungsten/s respectively). This increased activity observed over nano-WCx could be attributed to a greater predominance of W2C.