The oxidative coupling of methane (OCM) was investigated using a catalyst with a core@shell structure or a physical mixture comprised of MgO and SiC or Fe₃O₄, which was thermally activated via two different heating methods, namely, conventional resistive heating and microwave heating. The use of microwave radiation together with the catalyst structure was essential to achieve high reaction efficiency. The C₂ selectivity and yield were correlated with the presence of temperature gradients in the catalytic bed under microwave radiation. These thermal gradients and their distribution were experimentally evaluated using operando thermal visualization. Hotspots and thermal gradients were beneficial to achieve a higher CH₄ conversion; however, it was found that a uniform reactor temperature was crucial to attain a high C₂ yield in OCM and the core@shell structure is beneficial. The hypothesis that an enhanced OCM performance can be achieved by keeping the catalyst material hot and the gas cold, using microwave to prevent uncontrolled gas-phase reactions was supported by a kinetic study and experimentally demonstrated.

Oxidative dehydrogenation of ethane (ODHE) is an essential reaction in modern society to produce ethylene. The orthorhombic Mo₃VO_x catalyst (MoVO) was reported as one of the best catalysts for this reaction after a particular redox treatment to generate lattice oxygen defects. This study elucidates the location and nature of the defect sites as well as how molecular oxygen is activated toward the ODHE. The insights into the active site formation and guidelines for its design were gained through structural characterization, quantification of oxygen defects, and experimental and theoretical investigation of the reaction mechanisms. Peroxo formed at the defect sites of the bridging oxygen facing the heptagonal channel was found to drive the reaction efficiently.

The application of a polymer electrolyte membrane (PEM) electrolytic cell for continuous conversion of nitrate, one of the contaminants in water, to ammonia at the cathode was explored in the present work. Among carbon-supported metal (Cu, Ru, Rh and Pd) electrocatalysts, the Ru-based catalyst showed the best performance. By suppressing the competing hydrogen evolution reaction at the cathode, it was possible to reach 94 % faradaic efficiency for nitrate reduction towards ammonium. It was important to match the rate of the anodic reaction with the cathodic reaction to achieve high faradaic efficiency. By recirculating the effluent stream, 93 % nitrate conversion was achieved in 8 h of constant current electrolysis at 10 mA cm⁻² current density. The presented approach offers a promising path towards precious NH₃ production from nitrate-containing water that needs purification or can be obtained after capture of gaseous NO_x pollutants into water, leading to waste-to-value conversion.

The direct conversion of CO₂to CH₃OH represents an appealing strategy for the mitigation of anthropogenic CO₂emissions. Here, we report that small, narrowly distributed alloyed PdGa nanoparticles, prepared via surface organometallic chemistry from silica-supported Ga^IIIisolated sites, selectively catalyze the hydrogenation of CO₂to CH₃OH. At 230 °C and 25 bar, high activity (22.3 mol_MeOHmol_Pd^-1h^-1) and selectivity for CH₃OH/DME (81%) are observed, while the corresponding silica-supported Pd nanoparticles show low activity and selectivity. X-ray absorption spectroscopy (XAS), IR, NMR, and scanning transmission electron microscopy-energy-dispersive X-ray provide evidence for alloying in the as-synthesized material. In situ XAS reveals that there is a dynamic dealloying/realloying process, through Ga redox, while operando diffuse reflectance infrared Fourier transform spectroscopy demonstrates that, while both methoxy and formate species are observed in reaction conditions, the relative concentrations are inversely proportional, as the chemical potential of the gas phase is modulated. High CH₃OH selectivities, across a broad range of conversions, are observed, showing that CO formation is suppressed for this catalyst, in contrast to reported Pd catalysts.

The reaction pathway of high-pressure CO₂ hydrogenation over a Cu/ZnO/Al₂O₃ catalyst is investigated through the gradients of reactants/products concentration and catalyst temperature within the catalytic reactor. This study reveals that methanol is formed through direct CO₂ hydrogenation at low temperature, while above 260 °C methanol formation is mediated via CO which is formed by reverse water-gas shift reaction.

We should not underestimate the role of in situ and operando spectroscopic techniques in increasing our level of understanding of chemical reactions. The electrochemical reduction of CO2 is not an exception. The application of analytical techniques such as infrared spectroscopy, Raman spectroscopy, X-ray absorption spectroscopy and UV-vis spectroscopy over the years has been crucial for investigating the oxidation state changes of the electrode materials, identifying active surface species, understanding reaction mechanisms and deriving selectivity trends. Hence, such tools are indispensable for the rational design of electrocatalytic materials. This chapter presents an overview of the main spectroscopic techniques that can be applied to the investigation of homogeneous and heterogeneous electrochemical reduction of CO2, notable cell designs for spectroelectrochemical experiments, as well as highlighting representative reports on the use of various techniques.