Comparison of Methodologies of Activation Barrier Measurements for Reactions with Deactivation

Methodologies of activation barrier measurements for reactions with deactivation were theoretically analyzed. Reforming of ethane with CO₂ was introduced as an example for reactions with deactivation to experimentally evaluate these methodologies. Both the theoretical and experimental results showed that due to catalyst deactivation, the conventional method would inevitably lead to a much lower activation barrier, compared to the intrinsic value, even though heat and mass transport limitations were excluded. In this work, an optimal method was identified in order to provide a reliable and efficient activation barrier measurement for reactions with deactivation

Identification of the Intrinsic Active Site in Phase-Pure M1 Catalysts for Oxidation Dehydrogenation of Ethane by Density Functional Theory Calculations

Heterogeneous catalysts for alkane conversion reactions are required to possess both high activity for C–H bond cleavage and selectivity to target products. This work employed an atomic substitution strategy to investigate the active site of the phase-pure M1 MoVNbTeOx catalyst for the oxidation dehydrogenation of ethane (ODHE) reaction. Density of states and crystal orbital Hamilton population (COHP) based on density functional theory calculations indicated that the transition metal–O (M–O) bonds were weakened after H adsorption. Both integrated COHP and Bader charge were useful descriptors to correlate the electronic structure with catalytic performance. The results showed that the content of V in phase-pure M1 catalysts had a linear relationship with ethane conversion. Synergetic interactions between Te–O and V–O sites were accordingly considered as the intrinsic active sites for the ODHE reaction

Optimizing Binding Energies of Key Intermediates for CO₂ Hydrogenation to Methanol over Oxide-Supported Copper

Rational optimization of catalytic performance has been one of the major challenges in catalysis. Here we report a bottom-up study on the ability of TiO₂ and ZrO₂ to optimize the CO₂ conversion to methanol on Cu, using combined density functional theory (DFT) calculations, kinetic Monte Carlo (KMC) simulations, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements, and steady-state flow reactor tests. The theoretical results from DFT and KMC agree with in situ DRIFTS measurements, showing that both TiO₂ and ZrO₂ help to promote methanol synthesis on Cu via carboxyl intermediates and the reverse water–gas-shift (RWGS) pathway; the formate intermediates, on the other hand, likely act as a spectator eventually. The origin of the superior promoting effect of ZrO₂ is associated with the fine-tuning capability of reduced Zr³⁺ at the interface, being able to bind the key reaction intermediates, e.g. *CO₂, *CO, *HCO, and *H₂CO, moderately to facilitate methanol formation. This study demonstrates the importance of synergy between theory and experiments to elucidate the complex reaction mechanisms of CO₂ hydrogenation for the realization of a better catalyst by design

Reducing Iridium Loading in Oxygen Evolution Reaction Electrocatalysts Using Core–Shell Particles with Nitride Cores

The oxygen evolution reaction (OER) has broad applications in electrochemical devices, but it often requires expensive and scarce Ir-based catalysts in acid electrolyte. Presented here is a framework to reduce Ir loading by combining core–shell iridium/metal nitride morphologies using in situ experiments and density functional theory (DFT) calculations. Several group VIII transition metal (Fe, Co, and Ni) nitrides are studied as core materials, with Ir/Fe₄N core–shell particles showing enhancement in both OER activity and stability. In situ X-ray absorption fine structure measurements are used to determine the structure and stability of the core–shell catalysts under OER conditions. DFT calculations are used to demonstrate adsorbate binding energies as descriptors of the observed activity trends

Dry Reforming of Ethane and Butane with CO₂ over PtNi/CeO₂ Bimetallic Catalysts

Dry reforming is a potential process to convert CO₂ and light alkanes into syngas (H₂ and CO), which can be subsequently transformed to chemicals and fuels. In this work, PtNi bimetallic catalysts have been investigated for dry reforming of ethane and butane using both model surfaces and supported powder catalysts. The PtNi bimetallic catalyst shows an improvement in both activity and stability in comparison to the corresponding monometallic catalysts. The formation of PtNi alloy and the partial reduction of Ce⁴⁺ to Ce³⁺ under reaction conditions are demonstrated by in situ ambient-pressure X-ray photoemission spectroscopy (AP-XPS), X-ray diffraction (XRD), and X-ray absorption fine structure (XAFS) measurements. A Pt-rich bimetallic surface is revealed by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) following CO adsorption. Combined in situ experimental results and density functional theory (DFT) calculations suggest that the Pt-rich PtNi bimetallic surface structure would weaken the binding of surface oxygenate/carbon species and reduce the activation energy for C–C bond scission, leading to an enhanced dry reforming activity

Growth of Nanoparticles with Desired Catalytic Functions by Controlled Doping-Segregation of Metal in Oxide

The size and morphology of metal nanoparticles (NPs) often play a critical role in defining the catalytic performance of supported metal nanocatalysts. However, common synthetic methods struggle to produce metal NPs of appropriate size and morphological control. Thus, facile synthetic methods that offer controlled catalytic functions are highly desired. Here we have identified a new pathway to synthesize supported Rh nanocatalysts with finely tuned spatial dimensions and controlled morphology using a doping-segregation method. We have analyzed their structure evolutions during both the segregation process and catalytic reaction using a variety of in situ spectroscopic and microscopic techniques. A correlation between the catalytic functional sites and activity in CO₂ hydrogenation over supported Rh nanocatalysts is then established. This study demonstrates a facile strategy to design and synthesize nanocatalysts with desired catalytic functions

Identifying Dynamic Structural Changes of Active Sites in Pt–Ni Bimetallic Catalysts Using Multimodal Approaches

Alloy nanoparticle catalysts are known to afford unique activities that can differ markedly from their parent metals, but there remains a generally limited understanding of the nature of their atomic (and likely dynamic) structures as exist in heterogeneously supported forms under reaction conditions. Notably unclear is the nature of their active sites and the details of the varying oxidation states and atomic arrangements of the catalytic components during chemical reactions. In this work, we describe multimodal methods that provide a quantitative characterization of the complex heterogeneity present in the chemical and electronic speciations of Pt–Ni bimetallic catalysts supported on mesoporous silica during the reverse water gas shift reaction. The analytical protocols involved a correlated use of in situ X-ray Absorption Spectroscopy (XAS) and Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS), complimented by ex-situ aberration corrected Scanning Transmission Electron Microscopy (STEM). The data reveal that complex reactions occur between the metals and support in this system under operando conditions. These reactions, and the specific impacts of strong metal–silica bonding interactions, prevent the formation of alloy phases containing Ni–Ni bonds. This feature of structure provides high activity and selectivity for the reduction of CO₂ to carbon monoxide without significant competitive levels of methanation. We show how these chemistries evolve to the active state of the catalyst: bimetallic nanoparticles possessing an intermetallic structure (the active phase) that are conjoined with Ni-rich, metal-silicate species