Model-Based Design of Experiments for Temporal Analysis of Products (TAP): A Simulated Case Study in Oxidative Propane Dehydrogenation.

Temporal analysis of products (TAP) reactors enable experiments that probe numerous kinetic processes within a single set of experimental data through variations in pulse intensity, delay, or temperature. Selecting additional TAP experiments often involves an arbitrary selection of reaction conditions or the use of chemical intuition. To make experiment selection in TAP more robust, we explore the efficacy of model-based design of experiments (MBDoE) for precision in TAP reactor kinetic modeling.

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.

Formation of Surface Impurities on Lithium-Nickel-Manganese-Cobalt Oxides in the Presence of CO and HO.

Surface impurities involving parasitic reactions and gas evolution contribute to the degradation of high Ni content LiNiMnCoO (NMC) cathode materials. The transient kinetic technique of temporal analysis of products (TAP), density functional theory, and infrared spectroscopy have been used to study the formation of surface impurities on varying nickel content NMC materials (NMC811, NMC622, NMC532, NMC433, NMC111) in the presence of CO and HO. CO reactivity on a clean surface as characterized by CO conversion rate in the TAP reactor follows the order: NMC811 > NMC622 > NMC532 > NMC433 > NMC111.

Rate/Concentration Kinetic Petals: A Transient Method to Examine the Interplay of Surface Reaction Processes.

Transient pulse response experiments are used to construct rate/concentration kinetic dependencies, RC Petals and provide a new method to distinguish the timing and interplay of adsorption, surface reaction, and product formation on complex (industrial) materials. A petal shape arises as the dynamic "reaction-diffusion" experiment forces the concentration and reaction rate to return to zero. In contrast to the typical steady-state "Langmuir-type" RC dependence, RC petals have two branches, which arise as a result of decoupled gas and surface concentrations in the non-steady-state regime.

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.

Active site densities, oxygen activation and adsorbed reactive oxygen in alcohol activation on npAu catalysts.

The activation of molecular O2 as well as the reactivity of adsorbed oxygen species is of central importance in aerobic selective oxidation chemistry on Au-based catalysts. Herein, we address the issue of O2 activation on unsupported nanoporous gold (npAu) catalysts by applying a transient pressure technique, a temporal analysis of products (TAP) reactor, to measure the saturation coverage of atomic oxygen, its collisional dissociation probability, the activation barrier for O2 dissociation, and the facility with which adsorbed O species activate methanol, the initial step in the catalytic cycle of esterification. The results from these experiments indicate that molecular O2 dissociation is associated with surface silver, that the density of reactive sites is quite low, that adsorbed oxygen atoms do not spill over from the sites of activation onto the surrounding surface, and that methanol reacts quite facilely with the adsorbed oxygen atoms.