Methanol Formation Research Articles

In Situ Spectroscopic Characterization and Theoretical Calculations Identify Partially Reduced ZnO1−x/Cu Interfaces for Methanol Synthesis from CO2

AbstractThe active site of the industrial Cu/ZnO/Al2O3 catalyst used in CO2 hydrogenation to methanol has been debated for decades. Grand challenges remain in the characterization of structure, composition, and chemical state, both microscopically and spectroscopically, and complete theoretical calculations are limited when it comes to describing the intrinsic activity of the catalyst over the diverse range of structures that emerge under realistic conditions. Here a series of inverse model catalysts of ZnO on copper hydroxide were prepared where the size of ZnO was precisely tuned from atomically dispersed species to nanoparticles using atomic layer deposition. ZnO decoration boosted methanol formation to a rate of 877 gMeOH kgcat−1 h−1 with ≈80 % selectivity at 493 K. High pressure in situ X‐ray absorption spectroscopy demonstrated that the atomically dispersed ZnO species are prone to aggregate at oxygen‐deficient ZnO ensembles instead of forming CuZn metal alloys. By modeling various potential active structures, density functional theory calculations and microkinetic simulations revealed that ZnO/Cu interfaces with oxygen vacancies, rather than stoichiometric interfaces, Cu and CuZn alloys were essential to catalytic activation.

Hollow structured Cu@ZrO2 derived from Zr-MOF for selective hydrogenation of CO2 to methanol

The development of a highly efficient catalyst for CO2 activation and selective conversion to methanol is critical to address the issues associated with the high thermal stability of CO2 and controllable synthesis of methanol. Cu-based catalysts have been widely studied because of the low cost and excellent performance in mild conditions. However, the improvement of catalytic activity and selectivity remains challenging. Herein, we prepared hollow Cu@ZrO2 catalysts through pyrolysis of Cu-loaded Zr-MOF for CO2 hydrogenation to methanol. Low-temperature pyrolysis generated highly dispersed Cu nanoparticles with balanced Cu0/Cu+ sites, larger amounts of surface basic sites and abundant Cu-ZrO2 interface in the hollow structure, contributing to enhanced catalytic capacity for adsorption/activation of CO2 and selective hydrogenation to methanol. In situ Fourier Transform Infrared Spectroscopy revealed the methanol formation followed the formate-intermediated pathway. This work would provide a guideline for the design of high-performance catalysts and the understanding of the mechanism and active sites for CO2 hydrogenation to methanol.

On the Existence and Role of Formaldehyde During Aqueous Electrochemical Reduction of Carbon Monoxide to Methanol by Cobalt Phthalocyanine.

A long-time challenge in aqueous CO2 electrochemical reduction is to catalyze the formation of products beyond carbon monoxide with selectivity. Formaldehyde is the simplest of these products and one of the most relevant due to its broad use in the industry. Paradoxically it is one of the less reported product. Such scarcity may be in part explained by difficult identification and quantification using conventional chromatography or proton nuclear magnetic resonance techniques. Likewise, indirect detection methods are usually not compatible with labelled studies for asserting product origin. Recently, the possible production of formaldehyde during electrochemical reduction of carbon monoxide to methanol at cobalt phthalocyanine molecular catalyst in basic media has been the object of contradictory reports. By applying an analytical procedure based on proton NMR along with labelled studies, we provide definitive evidence for HCHO formation. We have further identified the possible scenarios for methanol formation through formaldehyde and revealed that the formation of the intermediate and its subsequent reduction are taking place at the same single active site. These studies open a new perspective to improve selectivity toward formaldehyde formation and to develop a subsequent chemistry based on reacting it with nucleophiles.

Biochemical mechanism underlying the pathogenesis of diabetic retinopathy and other diabetic complications in humans: the methanol-formaldehyde-formic acid hypothesis.

Hyperglycemia in diabetic patients is associated with abnormally-elevated cellular glucose levels. It is hypothesized that increased cellular glucose will lead to increased formation of endogenous methanol and/or formaldehyde, both of which are then metabolically converted to formic acid. These one-carbon metabolites are known to be present naturally in humans, and their levels are increased under diabetic conditions. Mechanistically, while formaldehyde is a cross-linking agent capable of causing extensive cytotoxicity, formic acid is an inhibitor of mitochondrial cytochrome oxidase, capable of inducing histotoxic hypoxia, ATP deficiency and cytotoxicity. Chronic increase in the production and accumulation of these toxic one-carbon metabolites in diabetic patients can drive the pathogenesis of ocular as well as other diabetic complications. This hypothesis is supported by a large body of experimental and clinical observations scattered in the literature. For instance, methanol is known to have organ- and species-selective toxicities, including the characteristic ocular lesions commonly seen in humans and non-human primates, but not in rodents. Similarly, some of the diabetic complications (such as ocular lesions) also have a characteristic species-selective pattern, closely resembling methanol intoxication. Moreover, while alcohol consumption or combined use of folic acid plus vitamin B is beneficial for mitigating acute methanol toxicity in humans, their use also improves the outcomes of diabetic complications. In addition, there is also a large body of evidence from biochemical and cellular studies. Together, there is considerable experimental support for the proposed hypothesis that increased metabolic formation of toxic one-carbon metabolites in diabetic patients contributes importantly to the development of various clinical complications.

Using Light and Electrons to Bend Carbon Dioxide: Developing and Understanding Catalysts for CO2 Conversion to Fuels and Feedstocks.

Our global society generates an unwieldy amount of CO2 per unit time. Therefore, the capture of this greenhouse gas must involve a diverse set of strategies. One solution to this problem is the conversion of CO2 into a more useful chemical species. Again, a multiplicity of syntheses and products will be necessary. No matter how elegant the chemistry is, commercial markets often have little use for a small set of compounds made in tremendous yield. Following this reasoning, the Bocarsly Research Group seeks to develop new electrochemical and photochemical processes that may be of utility in the conversion of CO2 to organic compounds. We focus on investigating proton-coupled charge transfer mechanisms that produce both C1 and carbon-carbon bonded products (C2+).In early work, we considered the reduction of CO2 to formate at electrocatalytic indium and tin electrodes. These studies demonstrated the key role of surface oxides in catalyzing the reduction of CO2. This work generated efficient systems for the formation of formate and paved the way to studies using non-copper, intermetallic electrocatalysts for the generation of C2+ species. Most notable is the efficient formation of oxalate at an oxidized Cr3Ga electrode. Oxalate has recently been suggested as a potential nonfossil, alternate organic feedstock.Separately, we have focused on the electrocatalytic effects of pyridine on the reduction of CO2 in aqueous electrolyte. These studies demonstrated that electrodes that normally yield a low hydrogen overpotential (Pd and Pt) show suppressed H2 evolution and strongly enhanced activity for CO2 reduction in the presence of pyridinium. Methanol was observed to form in high Faradaic yield at low overpotential using this system. The 6-electron, 6-proton reduction of CO2 in the presence of pyridinium was intriguing, and significant effort was placed on understanding the mechanism of this reaction both on metal electrodes and on semiconducting photocathodes. P-GaP electrodes were found to provide exceptional behavior for the formation of methanol using only light as the energy source.The pyridinium studies highlighted the role of protons in the overall reduction of CO2, stimulating our interest in the chemistry of MnBr(bpy)(CO)3 and related compounds. This complex was reported to electrochemically reduce CO2 to CO. We saw these reports as an opportunity to study the detailed nature of the proton-coupled electron transfer (PCET) mechanism associated with CO2 reduction. Our investigation of this system revealed the role of hydrogen-bonding in CO2 reduction and pointed the way for the construction of a photochemical process for CO generation using a [(bpy)(CO)3Mn(CN)Mn(bpy)(CO)3]+ photocatalyst.Based on our studies to date, it appears likely that heterogeneous systems can be assembled to convert CO2 into products that are "beyond C2 products." This may open up new practical chemistry in the area of fossil-based replacements for both synthesis and fuels. Systems with pragmatic efficiencies are close to reality. Electrochemical reactors using heterogeneous electrocatalysts show the stability and product selectivity needed to generate industrial opportunities. Continued growth of mechanistic understanding is expected to facilitate the chemical design of cogent systems for the taming of CO2.

Catalytic Reduction of Carbon Dioxide on the (001), (011), and (111) Surfaces of TiC and ZrC: A Computational Study.

We present a computational study of the activity and selectivity of early transition-metal carbides as carbon dioxide reduction catalysts. We analyze the effects of the adsorption of CO2 and H2 on the (001), (011), and metal-terminated (111) surfaces of TiC and ZrC, as carbon dioxide undergoes either dissociation to CO or hydrogenation to COOH or HCOO. The relative stabilities of the three reduction intermediates and the activation energies for their formation allow the identification of favored pathways on each surface, which are examined as they lead to the release of CO, HCOOH, CH3OH, and CH4, thereby also characterizing the activity and selectivity of the two materials. Reaction energetics implicate HCO as the key common intermediate on all surfaces studied and rule out the release of formaldehyde. Surface hydroxylation is shown to be highly selective toward methane production as the formation of methanol is hindered on all surfaces by its barrierless conversion to CO.

Enhanced Methanol Production over Non-promoted Cu–MgO–Al2O3 Materials with Ex-solved 2 nm Cu Particles: Insights from an Operando Spectroscopic Study

Enhanced methanol production is obtained over a non-promoted Cu–MgO–Al2O3 mixed oxide catalyst derived from a Cu–Mg–Al hydrotalcite precursor (HT) containing narrowly distributed small Cu NPs (2 nm). Conversions close to the equilibrium (∼20%) with a methanol selectivity of 67% are achieved at 230 °C, 20 bar, and a space velocity of 571 mL·gcat–1·h–1. Based on operando spectroscopic studies, the striking activity of this Cu-based catalyst is ascribed to the stabilization of Cu+ ions favored under reaction conditions due to lattice reorganization associated with the “HT-memory effect” promoted by water. Temperature-resolved infrared–mass spectrometry experiments have enabled the discernment of monodentate formate species, stabilized on Cu+ as the intermediate in methanol synthesis, in line with the results of density functional theory calculations. These monodentate formate species are much more reactive than bridge formate species, the latter ones behaving as intermediates in methane and CO formation. Moreover, poisoning of the Cu0 surface by strongly adsorbed species behaving as spectators is observed under reaction conditions. This work presents a detailed spectroscopic study highlighting the influence of the reaction pressure on the stabilization of active surface sites, and the possibility of enhancing methanol production on usually less active non-promoted nano-sized copper catalysts, provided that the proper support is selected, allowing the stabilization of doped Cu+. Thus, a methanol formation rate of 2.6 × 10–3 molMeOH·gcat–1·h–1 at 230 °C, 20 bar, and WHSV = 28 500 mL·gcat–1·h–1 is obtained on the Cu–MgO–Al2O3 HT-derived catalyst with 71% methanol selectivity, compared to 2.2 × 10–4 molMeOH·gcat–1·h–1 with 54% methanol selectivity obtained on a reference Cu/(Al2O3/MgO) catalyst not derived from a HT structure.

Biomimetic Metal-Free Hydride Donor Catalysts for CO2 Reduction

The catalytic reduction of carbon dioxide to fuels and value-added chemicals is of significance for the development of carbon recycling technologies. One of the main challenges associated with catalytic CO2 reduction is product selectivity: the formation of carbon monoxide, molecular hydrogen, formate, methanol, and other products occurs with similar thermodynamic driving forces, making it difficult to selectively reduce CO2 to the target product. Significant scientific effort has been aimed at the development of catalysts that can suppress the undesired hydrogen evolution reaction and direct the reaction toward the selective formation of the desired products, which are easy to handle and store. Inspired by natural photosynthesis, where the CO2 reduction is achieved using NADPH cofactors in the Calvin cycle, we explore biomimetic metal-free hydride donors as catalysts for the selective reduction of CO2 to formate. Here, we outline our recent findings on the thermodynamic and kinetic parameters that control the hydride transfer from metal-free hydrides to CO2. By experimentally measuring and theoretically calculating the thermodynamic hydricities of a range of metal-free hydride donors, we derive structural and electronic factors that affect their hydride-donating abilities. Two dominant factors that contribute to the stronger hydride donors are identified to be (i) the stabilization of the positive charge formed upon HT via aromatization or by the presence of electron-donating groups and (ii) the destabilization of hydride donors through the anomeric effect or in the presence of significant structural constrains in the hydride molecule. Hydride donors with appropriate thermodynamic hydricities were reacted with CO2, and the formation of the formate ion (the first reduction step in CO2 reduction to methanol) was confirmed experimentally, providing an important proof of principle that organocatalytic CO2 reduction is feasible. The kinetics of hydride transfer to CO2 were found to be slow, and the sluggish kinetics were assigned in part to the large self-exchange reorganization energy associated with the organic hydrides in the DMSO solvent. Finally, we outline our approaches to the closure of the catalytic cycle via the electrochemical and photochemical regeneration of the hydride (R-H) from the conjugate hydride acceptors (R+). We illustrate how proton-coupled electron transfer can be efficiently utilized not only to lower the electrochemical potential at which the hydride regeneration takes place but also to suppress the unwanted dimerization that neutral radical intermediates tend to undergo. Overall, this account provides a summary of important milestones achieved in organocatalytic CO2 reduction and provides insights into the future research directions needed for the discovery of inexpensive catalysts for carbon recycling.

Evaluation of Au/ZrO2 Catalysts Prepared via Postsynthesis Methods in CO2 Hydrogenation to Methanol

Au nanoparticles supported on ZrO2 enhance its surface acidic/basic properties to produce a high yield of methanol via the hydrogenation of CO2. Amorphous ZrO2-supported 0.5–1 wt.% Au catalysts were synthesized by two methods, namely deposition precipitation (DP) and impregnation (IMP), characterized by a variety of techniques, and evaluated in the process of CO2 hydrogenation to methanol. The DP-method catalysts were highly advantageous over the IMP-method catalyst. The DP method delivered samples with a large surface area, along with the control of the Au particle size. The strength and number of acidic and basic sites was enhanced on the catalyst surface. These surface changes attributed to the DP method greatly improved the catalytic activity when compared to the IMP method. The variations in the surface sites due to different preparation methods exhibited a huge impact on the formation of important intermediates (formate, dioxymethylene and methoxy) and their rapid hydrogenation to methanol via the formate route, as revealed by means of in situ DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy) analysis. Finally, the rate of formation of methanol was enhanced by the increased synergy between the metal and the support.

Theoretical investigation of methane oxidation reaction over a novel metal-free catalyst biphenylene network

Since graphene was discovered in 2004, two-dimensional (2D) carbon materials have been investigated for many applications including as energy storage materials, gas sensors, and heterogeneous catalysts. Recently, a new type of carbon material, termed a biphenylene network has been successfully synthesized, and consists of four-, six- and eight-membered rings in its structure. In this work, we perform density functional theory (DFT) calculations to study the methane oxidation reaction on a pristine biphenylene network nanosheet to understand its catalytic property. We found that the four-membered ring of the biphenyl network nanosheet possesses much stronger catalytic activity for O2 decomposition and methane conversion to methanol than does the pristine graphene nanosheet. In addition, our results show that both methanol formation and formyl aldehyde formation mechanisms can occur on the biphenyl network nanosheet. Methanol formation is a kinetic reaction control process at 500 K, while the formyl aldehyde formation is the thermodynamic reaction control process at a higher temperature of 600 K. Thus, the operating temperatures will control the selectivity of methane oxidation reaction on the biphenyl network nanosheet. This finding shows that the pure carbon material biphenyl network nanosheet might be an excellent metal-free catalyst for methane oxidation reactions.

Role of single-atom Pd in Cu/ZrO2 catalysts for CO2 hydrogenation to methanol

This study is to load the sing-atom Pd on Cu/ZrO2 with ion exchange method, and the role of Pd in Cu/ZrO2 for CO2 hydrogenation to methanol is investigated. The exchange of Pd with Cu/ZrO2 increase the methanol production rate from 223 μmol g−1 h−1 to 512 μmol g−1 h−1 at relatively mild conditions (1.5 Mpa, 260 °C). This exchange increases the splitting H adsorptions on Cu species, and strengthen interactions between Cu species and oxygen vacancies at the interface, thus promoting the formations of Cuδ+ species, which is critical to the formation of methanol. This study provides a promising alternative for the understandings the role of exchanged Pd in the Pd-Cu/ZrO2 catalysts for CO2 hydrogenation to methanol.

Methanol mediated direct CO2 hydrogenation to hydrocarbons: Experimental and kinetic modeling study

Carbon dioxide can be utilized as a feedstock to produce chemicals and renewable fuels sustainably. CO2 hydrogenation to hydrocarbons through a methanol mediated pathway requires a more detailed study, examining interactions between reaction processes leading to different product selectivities. In this particular work, we propose a kinetic model for the direct CO2 hydrogenation to different hydrocarbon products over an In2O3/HZSM-5 bifunctional catalytic bed. The model includes a CO2 hydrogenation to methanol model based on a Langmuir Hinshelwood Hougen Watson (LHHW) reaction mechanism over In2O3 catalyst combined with a lump-type methanol to hydrocarbon (MTH) model over the HZSM-5 zeolite. Interestingly, the combined model could largely predict the suppression of the reverse water gas shift (RWGS) reaction and an increase in the yield of hydrocarbons compared to the formation of methanol in case of the same reaction conditions carried out with only the methanol synthesis catalyst (In2O3). Further, by varying the mass ratio of the individual components of the bifunctional catalytic bed, it was demonstrated that a higher outlet concentration of methanol achieved with a higher mass ratio of the methanol synthesis catalyst caused less suppression of the RWGS reaction and shifted the hydrocarbon product distribution to a slightly larger share of higher hydrocarbons. These changes in product selectivity caused by variation of the catalyst mass ratio were both also successfully reproduced by the model. Therefore, a comparison between the experimental results and the model predictions shows that this model, including equilibrium effects for the reactions, can accurately predict the trends of the experimental findings for direct CO2 hydrogenation to hydrocarbons over the In2O3/HZSM-5 catalyst.

Cu-Ga3+-doped wurtzite ZnO interface as driving force for enhanced methanol production in co-precipitated Cu/ZnO/Ga2O3 catalysts

A detailed understanding of the interactions among the active components in gallium promoted Cu/ZnO catalysts, depending on the speciation of the gallium, are reported using in situ/operando spectroscopic studies, and their effect in the CO2 hydrogenation to methanol unraveled. In this contribution, the promoting effect of Ga3+-doped in the wurtzite ZnO lattice of a Cu/ZnO/Ga2O3 catalyst is compared to that of a zinc gallate (ZnGa2O4) phase. Remarkably, a strong inhibition of CO formation, together with an enhanced methanol formation, are observed in the Ga3+-doped ZnO sample, specifically at conditions where the competitive reverse water gas shift reaction predominates. The catalytic performance has been correlated with the microstructure of the catalyst where a surface enrichment with reduced ZnOx species, together with the stabilization of positive charged copper species and an increase in the amount of surface basic sites for CO2 adsorption are observed on the most selective sample.

Photocatalytic reduction of CO2 to methanol using Zr(IV)-based MOF composite with g-C3N4 quantum dots under visible light irradiation

Considering the global warming due to the accumulation of excess CO2 in the atmosphere, it is vital to reduce the CO2emissions by capturing or converting it into value-added chemicals and fuels. Among the known materials, MOFs have great significance in capturing the CO2 and its conversion to energy efficient fuels due to its tuneability, high porosity, large surface area, unique structure, and semiconducting behavior. In the present study, graphitic carbon nitride quantum dots coupled Zr (IV) based MOF composite (g-CNQDs@MOF) has been reported for the photoreduction of CO2 to methanol selectively under visible light irradiation. Graphitic carbon nitride quantum dots (g-CNQDs) in the synthesized Zr-based MOF composite play an important role for photocatalytic CO2 reduction due to its rich photo properties thereby improving the electronic conductance properties of the composite. g-CNQDs in the Zr (IV)-based MOF composite acted as co-catalyst which enhanced the electron-hole separation by elongating the lifetime of photogenerated charge carriers on the surface of MOF composite. These excess electrons accelerated the generation of catalytically active sites on the composite’s surface to reduce CO2 selectively into methanol with better selectivity and efficient methanol formation rate.

X-Ray-induced Diffusion and Mixing in Layered Astrophysical Ices

Abstract Ice in cold cosmic environments is expected to be organized in a bilayered structure of polar and apolar components. The initial water-rich layer is embedded in an icy CO envelope, which provides the feedstock for methanol formation through hydrogenation. These two components are thought to be physically segregated, unless an increase in temperature favors mobility and reactivity within the ice. We present new and robust evidence of X-ray-induced diffusion within interstellar ice analogues at very low temperatures, leading to an efficient mixing of the molecular content of the ice. The results of our study have two main implications. First, molecular mixing enhances chemical reactions from which complex organic species, including many of prebiotic interest, are formed. Second, diffusion drives the desorption of species that would otherwise remain buried near the surface of dust, thus enhancing their abundances in the gas, where they can be detected in the radio-wave domain. Such a scenario may have implications for the chemical history of ices in protoplanetary disks, in particular in the early stages of their life.

CO2 Hydrogenation to Methanol over Cd4/TiO2 Catalyst: Insight into Multifunctional Interface.

Supported metal catalysts have shown to be efficient for CO2 conversion due to their multifunctionality and high stability. Herein, we have combined density functional theory calculations with microkinetic modeling to investigate the catalytic reaction mechanisms of CO2 hydrogenation to CH3OH over a recently reported catalyst of Cd4/TiO2. Calculations reveal that the metal‐oxide interface is the active center for CO2 hydrogenation and methanol formation via the formate pathway dominates over the reverse water‐gas shift (RWGS) pathway. Microkinetic modeling demonstrated that formate species on the surface of Cd4/TiO2 is the relevant intermediate for the production of CH3OH, and CH2O# formation is the rate‐determining step. These findings demonstrate the crucial role of the Cd‐TiO2 interface for controlling the CO2 reduction reactivity and CH3OH selectivity.

CO2 hydrogenation to methanol promoted by Cu and metastable tetragonal CexZryOz interface

Designing effective catalyst to improve the activity of CO2 hydrogenation to methanol is a potential avenue to realize the utilization of CO2 resources. Herein we construct three kinds of Cu/CexZryOz (CCZ) catalysts with different crystal phases of CexZryOz solid solutions, which demonstrate distinct activity and methanol selectivity in the order of metastable tetragonal-CCZ (CCZ-t″, parts of oxygen in CexZryOz were replaced by tetragonal phase from cubic fluorite phase) > tetragonal-CCZ (CCZ-t) > cubic-CCZ (CCZ-c) for CO2 hydrogenation to methanol. Structural analysis reveals that oxygen vacancies, surface hydroxyls and unsaturated Cu species of CCZ all follow the same sequence as that of activity and methanol selectivity, indicating that the above features are beneficial to improve the catalytic reaction performance. Temperature programmed experiments and mechanism studies show that the interface between Cu and tetragonal (t and t″) CexZryOz can promote CO2 adsorption, and the adsorbed CO2 is more reactive and can generate active bidentate carbonate species, which can be hydrogenated to form active monodentate and bidentate formate species under CO2 and H2 atmosphere. These intermediates should be crucial to the formation of methanol product. CCZ-t″ has stronger H2 activation ability than CCZ-t, which makes the former catalyst have more intermediates and higher methanol selectivity. In contrast, CO2 mainly adsorbs on cubic CexZryOz support of CCZ-c, but its H2 spillover ability is low, which hinders the reaction process. In addition, the strong adsorption of surface intermediates on CCZ-c is also not conducive to methanol formation. Results here demonstrate that constructing active Cu-support interfaces may be an important approach to design effective catalyst for CO2 hydrogenation.

Dynamics over a Cu-graphite electrode during the gas-phase CO2 reduction investigated by APXPS.

The electrocatalytic conversion of CO2 to fuels and chemicals using renewable energy is a key decarbonization technology. From a technological viewpoint, the realization of such process in the gas phase and at room temperature is considered advantageous as it allows one to circumvent the limited CO2 solubility in liquid electrolytes and CO2 transport across the electrical double layer. Yet, electrocatalysts' performances reported so far are promising but not satisfactory. To inform the design of new materials, in this study, we apply ambient pressure X-ray photoelectron and absorption spectroscopies coupled with on-line gas detection via mass spectrometry to investigate in situ performance and interface chemistry of an electrodeposited Cu on graphitic carbon support under conditions of CO2 reduction. We use the ISISS beamline at the synchrotron facility BESSY II of the HZB and the electrochemical cell based on polymeric electrolyte membrane previously developed. We show that under cathodic potential in which methanol is formed, a fraction of the electrode with a predominantly Cu(I) electronic structure undergoes reduction to metallic Cu. The C speciation is characterized by C-O and sp3 CH3 species whereas no atomic C was formed under this condition. We also show the important role of water in the formation of methanol from accumulated surface CH3 species.

Dependence of copper particle size and interface on methanol and CO formation in CO2 hydrogenation over Cu@ZnO catalysts

The copper particle size and the interface of Cu and ZnO showed strong impacts on the formation of methanol and CO in CO2 hydrogenation over Cu@ZnO catalysts.

Oxidative decomposition of dimethyl methylphosphonate on rutile TiO2(110): the role of oxygen vacancies.

The decomposition of dimethyl methylphosphonate (DMMP, (CH3O)2P(O)(CH3)), a simulant to the toxic nerve agent Sarin, on the rutile TiO2(110) surface has been studied with temperature programmed desorption (TPD) and density functional theory (DFT) calculations. The reactivity of the TiO2(110) surface for DMMP decomposition is shown to be low, with mainly molecular desorption and only a small fraction of methanol and formaldehyde decomposition products seen from TPD at around 650 K. In addition, this amount of products is similar to the number of O vacancies on the surface. DFT calculations show that O vacancies are key for P-OCH3 bond cleavage of DMMP, lowering the barrier by 0.7 eV and enabling the reactive process to occur at around 600 K. This is explained by the closer position of DMMP with respect to the surface in the presence of O vacancies. Calculations show that the produced methoxy groups can transform into gas phase formaldehyde and methanol at the considered temperature (600 K), in agreement with experiments. O-C bond cleavage of DMMP is also a viable pathway at such a high temperature (600 K) for DMMP decomposition on r-TiO2, even in the absence of O vacancies, but the formation of a gas phase product is energetically unfavorable. O vacancies hence are the active sites for decomposition of DMMP into gas phase products on r-TiO2(110).