CO2 hydrogenation to methanol at pressures up to 950bar

Ga and Zn increase the oxygen affinity of Cu-based catalysts for the CO x hydrogenation according to ab initio atomistic thermodynamics

The direct hydrogenation of CO or CO₂ to methanol, a highly vivid research area in the context of sustainable development, is typically carried out with Cu-based catalysts. Specific elements (so-called promoters) improve the catalytic performance of these systems under a broad range of reaction conditions (from pure CO to pure CO₂). Some of these promoters, such as Ga and Zn, can alloy with Cu and their role remains a matter of debate. In that context, we used periodic DFT calculations on slab models and ab initio thermodynamics to evaluate both metal alloying and surface formation by considering multiple surface facets, different promoter concentrations and spatial distributions as well as adsorption of several species (O*, H*, CO* and ) for different gas phase compositions. Both Ga and Zn form an fcc-alloy with Cu due to the stronger interaction of the promoters with Cu than with themselves. While the Cu-Ga-alloy is more stable than the Cu-Zn-alloy at low promoter concentrations (<25%), further increasing the promoter concentration reverses this trend, due to the unfavoured Ga-Ga-interactions. Under CO₂ hydrogenation conditions, a substantial amount of O* can adsorb onto the alloy surfaces, resulting in partial dealloying and oxidation of the promoters. Therefore, the CO₂ hydrogenation conditions are actually rather oxidising for both Ga and Zn despite the large amount of H₂ present in the feedstock. Thus, the growth of a GaO _x /ZnO _x overlayer is thermodynamically preferred under reaction conditions, enhancing CO₂ adsorption, and this effect is more pronounced for the Cu-Ga-system than for the Cu-Zn-system. In contrast, under CO hydrogenation conditions, fully reduced and alloyed surfaces partially covered with H* and CO* are expected, with mixed CO/CO₂ hydrogenation conditions resulting in a mixture of reduced and oxidised states. This shows that the active atmosphere tunes the preferred state of the catalyst, influencing the catalytic activity and stability, indicating that the still widespread image of a static catalyst under reaction conditions is insufficient to understand the complex interplay of processes taking place on a catalyst surface under reaction conditions, and that dynamic effects must be considered.

Hydrogenation of carbon dioxide (CO2) to fuels in microreactors: a review of set-ups and value-added chemicals production

A review of CO2 hydrogenation to fuels and value-added chemicals in microreactors.

State of art of valorising of diverse potential feedstocks for the production of alcohols and ethers: Current changes and perspectives

Alcohols could be the biggest factor for the improvement of world biofuel economy in the present century due to their excellent properties compared to petroleum products. The primary concerns of sustainable alcohol production for meeting the growing energy demand owing to the selection of viable feedstock and this might enhance the opportunities for developing numerous advanced techniques. In this review, the valorization of alcohol production from several production routes has been exposed by covering the traditional routes to the present state of the art technologies. Even though the fossil fuel conversion could be dominant method for methanol production, many recent innovations like photo electrochemical synthesis and electrolysis methods might play vital role in production of renewable methanol in future. There have been several production routes for production of ethanol and among which the fermentation of lignocellulose biomass would be the ultimate choice for large scale shoot up. The greenhouse gas recovery in the form of alcohols through electrochemistry technique and hydrogenation method are the important methods for commercialization of alcohols in future. It is also observed that algae based renewable bio-alcohols is highly influenced by carbohydrate content and sustainable approaches in algae conversion to bio-alcohols would bring greater demand in future market. There is a lack of innovation in higher alcohols production in single process and this could be bounded by combining dehydrogenation and decarboxylation techniques. Finally, this review enlists the opportunities and challenges of existing alcohols production and recommended the possible routes for making significant enhancement in production.

Recent advances in hydrogenation of CO2 into hydrocarbons via methanol intermediate over heterogeneous catalysts

This review provides recent advances in the conversion of CO₂ to methanol, methanol to hydrocarbons, and direct conversion of CO₂ to hydrocarbons via methanol intermediate over various monofunctional and bifunctional solid catalysts.

Towards a continuous formic acid synthesis: a two-step carbon dioxide hydrogenation in flow

The need for long term, large-scale storage solutions to match surplus renewable energy with demand drives technological innovation towards a low-carbon economy.

Challenges in the Greener Production of Formates/Formic Acid, Methanol, and DME by Heterogeneously Catalyzed CO2 Hydrogenation Processes

The recent advances in the development of heterogeneous catalysts and processes for the direct hydrogenation of CO₂ to formate/formic acid, methanol, and dimethyl ether are thoroughly reviewed, with special emphasis on thermodynamics and catalyst design considerations. After introducing the main motivation for the development of such processes, we first summarize the most important aspects of CO₂ capture and green routes to produce H₂. Once the scene in terms of feedstocks is introduced, we carefully summarize the state of the art in the development of heterogeneous catalysts for these important hydrogenation reactions. Finally, in an attempt to give an order of magnitude regarding CO₂ valorization, we critically assess economical aspects of the production of methanol and DME and outline future research and development directions.

Interplay between Reaction and Phase Behaviour in Carbon Dioxide Hydrogenation to Methanol

Condensation promotes CO₂ hydrogenation to CH₃ OH beyond equilibrium through in situ product separation. Although primordial for catalyst and reactor design, triggering conditions as well as the impact on sub-equilibrium reaction behaviour remain unclear. Herein we used an in-house designed micro-view-cell to gain chemical and physical insights into reaction and phase behaviour under high-pressure conditions over a commercial Cu/ZnO/Al₂ O₃ catalyst. Raman microscopy and video monitoring, combined with online gas chromatography analysis, allowed the complete characterisation of the reaction bulk up to 450 bar (1 bar=0.1 MPa) and 350 °C. Dew points of typical effluent streams related to a parametric study suggest that the improving reaction performance and reverting selectivities observed from 230 °C strongly correlate with (i) a regime transition from kinetic to thermodynamic, and (ii) a phase transition from a single supercritical to a biphasic reaction mixture. Our results advance a rationale behind transitioning CH₃ OH selectivities for an improved understanding of CO₂ hydrogenation under high pressure.

Synthesis of a Cu-infiltrated Zr-doped SBA-15 catalyst for CO2hydrogenation into methanol and dimethyl ether

A catalytically active nanoassembly comprising Cu-nanoparticles grown on integrated and active supports (large pore Zr-doped mesoporous SBA-15 silica) has been synthesized and used to promote CO₂hydrogenation.

Performance and characteristics of a high pressure, high temperature capillary cell with facile construction for operando x-ray absorption spectroscopy

We demonstrate the use of commercially available fused silica capillary and fittings to construct a cell for operando X-ray absorption spectroscopy (XAS) for the study of heterogeneously catalyzed reactions under high pressure (up to 200 bars) and high temperature (up to 280 °C) conditions. As the first demonstration, the cell was used for CO2 hydrogenation reaction to examine the state of copper in a conventional Cu/ZnO/Al2O3 methanol synthesis catalyst. The active copper component of the catalyst was shown to remain in the metallic state under supercritical reaction conditions, at 200 bars and up to 260 °C. With the coiled heating system around the capillary, one can easily change the length of the capillary and control the amount of catalyst under investigation. With precise control of reactant(s) flow, the cell can mimic and serve as a conventional fixed-bed micro-reactor system to obtain reliable catalytic data. This high comparability of the reaction performance of the cell and laboratory reactors is crucial to gain insights into the nature of actual active sites under technologically relevant reaction conditions. The large length of the capillary can cause its bending upon heating when it is only fixed at both ends because of the thermal expansion. The degree of the bending can vary depending on the heating mode, and solutions to this problem are also presented. Furthermore, the cell is suitable for Raman studies, nowadays available at several beamlines for combined measurements. A concise study of CO2 phase behavior by Raman spectroscopy is presented to demonstrate a potential of the cell for combined XAS-Raman studies.

Microfluidic studies of carbon dioxide

Carbon dioxide (CO2) sequestration, storage and recycling will greatly benefit from comprehensive studies of physical and chemical gas-liquid processes involving CO2. Over the past five years, microfluidics emerged as a valuable tool in CO2-related research, due to superior mass and heat transfer, reduced axial dispersion, well-defined gas-liquid interfacial areas and the ability to vary reagent concentrations in a high-throughput manner. This Minireview highlights recent progress in microfluidic studies of CO2-related processes, including dissolution of CO2 in physical solvents, CO2 reactions, the utilization of CO2 in materials science, and the use of supercritical CO2 as a "green" solvent.