New Mechanistic and Reaction Pathway Insights for Oxidative Coupling of Methane (OCM) over Supported Na WO /SiO Catalysts.

The complex structure of the catalytic active phase, and surface-gas reaction networks have hindered understanding of the oxidative coupling of methane (OCM) reaction mechanism by supported Na WO /SiO catalysts. The present study demonstrates, with the aid of in situ Raman spectroscopy and chemical probe (H -TPR, TAP and steady-state kinetics) experiments, that the long speculated crystalline Na WO active phase is unstable and melts under OCM reaction conditions, partially transforming to thermally stable surface Na-WO sites. Kinetic analysis via temporal analysis of products (TAP) and steady-state OCM reaction studies demonstrate that (i) surface Na-WO sites are responsible for selectively activating CH to C H and over-oxidizing CH to CO and (ii) molten Na WO phase is mainly responsible for over-oxidation of CH to CO and also assists in oxidative dehydrogenation of C H to C H .

Understanding Reaction Networks through Controlled Approach to Equilibrium Experiments Using Transient Methods.

We report a combined experimental/theoretical approach to studying heterogeneous gas/solid catalytic processes using low-pressure pulse response experiments achieving a controlled approach to equilibrium that combined with quantum mechanics (QM)-based computational analysis provides information needed to reconstruct the role of the different surface reaction steps. We demonstrate this approach using model catalysts for ammonia synthesis/decomposition. Polycrystalline iron and cobalt are studied via low-pressure TAP (temporal analysis of products) pulse response, with the results interpreted through reaction free energies calculated using QM on Fe-BCC(110), Fe-BCC(111), and Co-FCC(111) facets.

Active Site and Electronic Structure Elucidation of Pt Nanoparticles Supported on Phase-Pure Molybdenum Carbide Nanotubes.

We recently showed that phase-pure molybdenum carbide nanotubes can be durable supports for platinum (Pt) nanoparticles in hydrogen evolution reaction (HER). In this paper we further characterize surface properties of the same Pt/β-MoC catalyst platform using carbon monoxide (CO)-Pt and CO-MoC bond strength of different Pt particle sizes in the <3 nm range. Results from diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and temporal analysis of products (TAP) revealed the existence of different active sites as Pt particle size increases.