Bulk and supported MoSx materials have gained interest as alternative catalysts for light alkane dehydrogenation, but there is little kinetic data published with which rigorous comparisons can be made to other catalysts. Here, rates, selectivities, and activation barriers are collected under conditions of differential conversion for the dehydrogenation of isobutane over various morphologies of molybdenum sulfide. We find that a "rag-like" MoS2 composed of small, disordered crystallites exhibits higher catalytic rates than layered, highly crystalline MoS2 (52 vs 2.7 μmol ks-1 gcat -1 at 360 °C). This is in part not only due to increased surface area but also due to intrinsically more active edge and defect sites exposed by the rag-like structure, as shown by a decrease in apparent activation energy from 61 to 43 kJ mol-1. Supporting MoSx on metal oxides or metal organic frameworks gives small MoSx clusters that have up to 7-fold higher rates per mass of MoS2 than even the rag-like MoS2. Rates are support-dependent, with the highest rates per mass of MoS2 observed over MoSx/TiO2. Pt/Al2O3 has a 50-fold higher rate than the best MoS2 catalysts (2700 μmol ks-1 gcat -1 at 360 °C), but it has an apparent activation energy of 41 kJ mol-1, similar to that of the rag-like MoS2. Therefore, the rates over MoS2 appear to be limited by a small number of active sites on the surface, rather than intrinsically poor activity. Given the data provided in this manuscript and the enormous phase space available to metal sulfides, these materials warrant further investigation as alternative light alkane dehydrogenation catalysts, especially for use under conditions that would deactivate a precious metal catalyst.
ASJC Scopus subject areas
- Chemical Engineering(all)
- Industrial and Manufacturing Engineering