VOCs Photothermo-Catalytic Removal on MnOx-ZrO2 Catalysts

Solar photothermo-catalysis is a fascinating multi-catalytic approach for volatile organic compounds (VOCs) removal. In this work, we have explored the performance and the chemico-physical features of non-critical, noble, metal-free MnOx-ZrO2 mixed oxides. The structural, morphological, and optical characterizations of these materials pointed to as a low amount of ZrO2 favoured a good interaction and the ionic exchange between the Mn and the Zr ions. This favoured the redox properties of MnOx increasing the mobility of its oxygens that can participate in the VOCs oxidation through a Mars-van Krevelen mechanism. The further application of solar irradiation sped up the oxidation reactions promoting the VOCs total oxidation to CO2. The MnOx-5 wt.%ZrO2 sample showed, in the photothermo-catalytic tests, a toluene T90 (temperature of 90% of conversion) of 180 °C and an ethanol T90 conversion to CO2 of 156 °C, 36 °C, and 205 °C lower compared to the thermocatalytic tests, respectively. Finally, the same sample exhibited 84% toluene conversion and the best selectivity to CO2 in the ethanol removal after 5 h of solar irradiation at room temperature, a photoactivity similar to the most employed TiO2-based materials. The as-synthetized mixed oxide is promising for an improved sustainability in both catalyst design and environmental applications.

CO Oxidation Capabilities of La- and Nd-Based Perovskites

Catalytic tests to assess the performance of mixed perovskite-type oxides (La0.9Ca0.1FeO3-δ, La0.6Ca0.4FeO3-δ, Nd0.9Ca0.1FeO3-δ, Nd0.6Ca0.4FeO3-δ, Nd0.6Ca0.4Fe0.9Co0.1O3-δ, Nd0.6Ca0.4Fe0.97Ni0.03O3-δ, and LSF) with respect to CO oxidation are presented as well as characterization of the materials by XRD and SEM. Perovskites are a highly versatile class of materials due to their flexible composition and their ability to incorporate dopants easily. CO oxidation is a widely used “probe reaction” for heterogeneous catalysts. In this study, it is demonstrated how tuning the composition of the catalyst material (choice of A-site cation, A-site and B-site doping) greatly influences the activity. Changing the A-site cation to Nd3+ or increasing the concentration of Ca2+ as A-site dopant improves the performance of the catalyst. Additional B-site doping (e.g., Co) affects the performance as well—in the case of Co-doping by shifting ignition temperature to lower temperatures. Thus, perovskites offer an interesting approach to intelligent catalyst design and tuning the specific properties towards desired applications.

Influence of the Greater Protein Environment on the Electrostatic Potential in Metalloenzyme Active Sites: the Case of Formate Dehydrogenase

The Mo/W containing metalloenzyme formate dehydrogenase (FDH) is an efficient and selective natural catalyst which reversibly converts CO2 to formate under ambient conditions. A greater understanding of the role of the protein environment in determining the local properties of the FDH active site would enable rational bioinspired catalyst design. In this study, we investigate the impact of the greater protein environment on the electrostatic potential (ESP) of the active site. To model the enzyme environment, we used a combination of long-timescale classical molecular dynamics (MD) and multiscale quantum-mechanical/molecular-mechanical (QM/MM) simulations. We leverage the charge shift analysis method to systematically construct QM regions and analyze the electronic environment of the active site by evaluating the degree of charge transfer between the core active site and the protein environment. The contribution of the terminal chalcogen ligand to the ESP of the metal center is substantial and dependent on the chalcogen identity, with ESPs less negative and similar for Se and S terminal chalcogens than for O regardless of whether the Mo6+ or W6+ metal center is present. Our evaluation reveals that the orientation of the sidechains and ligand conformations will alter the relative trends in the ESP observed for a given metal center or terminal chalcogen, highlighting the importance of sampling dynamic fluctuations in the protein. Overall, our observations suggest that the terminal chalcogen ligand identity plays an important role in the enzymatic activity of FDH.

Understanding Catalytic Activity Trends of Electrochemical Ammonia Oxidation Reaction using Density Functional Theory Calculations and Microkinetic Modeling

Electrochemical ammonia oxidation reaction (AOR) is promising as an alternative anodic reaction to oxygen evolution in water electrolysis system. Herein, we develop a microkinetic model based on density functional theory (DFT) calculations for all possible reaction pathways considering both thermochemical and electrochemical N-N bond formation processes. From the microkinetic analysis, we discover that Faradaic bond formation contributes to AOR more significantly than non-Faradaic counterpart and we observe good agreements with the experimental results. We then construct a kinetic volcano plot using binding energies of two reaction intermediates as descriptors, which suggests a catalyst design strategy. Following this strategy, we enumerate numerous alloy combinations and identify a few promising candidates with higher catalytic activity than the most active monometallic Pt catalyst.

Computational Study of Catalytic Urethane Formation

Polyurethanes (PUs) are widely used in different applications, and thus various synthetic procedures including one or more catalysts are applied to prepare them. For PU foams, the most important catalysts are nitrogen-containing compounds. Therefore, in this work, the catalytic effect of eight different nitrogen-containing catalysts on urethane formation will be examined. The reactions of phenyl isocyanate (PhNCO) and methanol without and in the presence of catalysts have been studied and discussed using the G3MP2BHandHLYP composite method. The solvent effects have also been considered by applying the SMD implicit solvent model. A general urethane formation mechanism has been proposed without and in the presence of the studied catalysts. The proton affinities (PA) were also examined. The barrier height of the reaction significantly decreased (∆E0 > 100 kJ/mol) in the presence of the studied catalysts, which proves the important effect they have on urethane formation. The achieved results can be applied in catalyst design and development in the near future.

Review of the Hydrogen Evolution Reaction—A Basic Approach

An increasing emphasis on energy storage resulted in a surge of R&D efforts into producing catalyst materials for the hydrogen evolution reaction (HER) with emphasis on decreasing the usage of platinum group metal (PGMs). Alkaline water electrolysis holds promise for satisfying future energy storage demands, however the intrinsic potential of this technology is impeded by sluggish reaction kinetics. Here, we summarize the latest efforts within alkaline HER electrocatalyst design, where these efforts are divided between three catalyst design strategies inspired by the three prevailing theories describing the pH-dependence of the HER activity. Modifying the electronic structure of a host through codoping and creating specific sites for hydrogen/hydroxide adsorption stand out as promising strategies. However, with the vast amount of possible combinations, emphasis on screening parameters is important. The authors predict that creating a codoped catalyst using the first strategy by screening materials based on their hydrogen, hydroxide and water binding energies, and utilizing the second and third strategies as optimization parameters might yield both active and stable HER catalyst materials. This strategy has the potential to greatly advance the current status of alkaline water electrolysis as an energy storage option.

Moving Mountains: Reshaping the Activity Volcano of Electrocatalysis with Fluxional Subnano Clusters

The activity volcano derived from Sabatier analysis provides intuitive guide for catalyst design, but it also imposes fundamental limitations on the maximal activity and the pool of high-performance elements. Here we show that the activity volcano for oxygen reduction reaction (ORR) can be shifted and reshaped in the subnano regime. The fluxional behavior of subnano clusters, in both isolated and graphite-supported forms, not only breaks the linear scaling relationships but also causes an overall strengthening in adsorbate binding. The metals with optimal adsorbate binding in the bulk form (Pt/Pd) thus suffer over-binding issues, while the metals that under-bind in the bulk form (Ag/Au) gain optimal reaction energetics. In addition, the potential-dependence of isomer energies differ, causing non-linear reaction free energy-potential relations and enabling population-tuning of specific isomers, thereby surpassing the apex of the activity volcano. The shift of the volcano that puts under-binding elements closer to the top is likely general in fluxional cluster catalysis, and can be used for cluster catalyst design.