High-pressure advantages in stoichiometric hydrogenation of carbon dioxide to methanol

Carbon Dioxide Hydrogenation by Means of Plasmonic Resonance Activation in Silica Aerogel Media

Surface Plasmon Resonance can be used to activate zinc oxide/copper catalysts in order to perform the carbon dioxide hydrogenation reaction by means of light energy, avoiding high-temperature processes. The synthesis and impregnation methods have been designed to fill glass microreactors with ZnO/Cu nanoparticles supported on transparent silica aerogels to maximize the light absorbed by the catalyst. A LED device surrounding the glass microreactors provided white light to activate the catalyst homogeneously throughout the reactor. Temperature, pressure, amount of catalyst and gases flow were studied as possible variables to enhance the process trying to maximize CO₂ conversion rates, achieving the best results working at high pressures. The use of transparent SiO₂ Aerogels as supports for photocatalytic gas phase reactions even under high-pressure conditions is demonstrated.

Isolated Zr Surface Sites on Silica Promote Hydrogenation of CO2 to CH3OH in Supported Cu Catalysts

Copper nanoparticles supported on zirconia (Cu/ZrO₂) or related supported oxides (Cu/ZrO₂/SiO₂) show promising activity and selectivity for the hydrogenation of CO₂ to CH₃OH. However, the role of the support remains controversial because most spectroscopic techniques provide information dominated by the bulk, making interpretation and formulation of structure-activity relationships challenging. In order to understand the role of the support and in particular of the Zr surface species at a molecular level, a surface organometallic chemistry approach has been used to tailor a silica support containing isolated Zr(IV) surface sites, on which copper nanoparticles (∼3 nm) are generated. These supported Cu nanoparticles exhibit increased CH₃OH activity and selectivity compared to those supported on SiO₂, reaching catalytic performances comparable to those of the corresponding Cu/ZrO₂. Ex situ and in situ X-ray absorption spectroscopy reveals that the Zr sites on silica remain isolated and in their +4 oxidation state, while ex situ solid-state nuclear magnetic resonance spectroscopy and catalytic performances show that similar mechanisms are involved with the single-site support and ZrO₂. These observations imply that Zr(IV) surface sites at the periphery of Cu particles are responsible for promoting CH₃OH formation on Cu-Zr-based catalysts and provide a guideline to develop selective CH₃OH synthesis catalysts.

Ni-Sn-Supported ZrO2 Catalysts Modified by Indium for Selective CO2 Hydrogenation to Methanol

Ni and NiSn supported on zirconia (ZrO₂) and on indium (In)-incorporated zirconia (InZrO₂) catalysts were prepared by a wet chemical reduction route and tested for hydrogenation of CO₂ to methanol in a fixed-bed isothermal flow reactor at 250 °C. The mono-metallic Ni (5%Ni/ZrO₂) catalysts showed a very high selectivity for methane (99%) during CO₂ hydrogenation. Introduction of Sn to this material with the following formulation 5Ni5Sn/ZrO₂ (5% Ni-5% Sn/ZrO₂) showed the rate of methanol formation to be 0.0417 μmol/(g_cat·s) with 54% selectivity. Furthermore, the combination NiSn supported on InZrO₂ (5Ni5Sn/10InZrO₂) exhibited a rate of methanol formation 10 times higher than that on 5Ni/ZrO₂ (0.1043 μmol/(g_cat·s)) with 99% selectivity for methanol. All of these catalysts were characterized by X-ray diffraction, high-resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy (STEM), X-ray photoelectron spectroscopy, CO₂-temperature-programmed desorption, and density functional theory (DFT) studies. Addition of Sn to Ni catalysts resulted in the formation of a NiSn alloy. The NiSn alloy particle size was kept in the range of 10-15 nm, which was evidenced by HRTEM study. DFT analysis was carried out to identify the surface composition as well as the structural location of each element on the surface in three compositions investigated, namely, Ni₂₈Sn₂₇, Ni₁₈Sn₃₇, and Ni₃₇Sn₁₈ bimetallic nanoclusters, and results were in agreement with the STEM and electron energy-loss spectroscopy results. Also, the introduction of "Sn" and "In" helped improve the reducibility of Ni oxide and the basic strength of catalysts. Considerable details of the catalytic and structural properties of the Ni, NiSn, and NiSnIn catalyst systems were elucidated. These observations were decisive for achieving a highly efficient formation rate of methanol via CO₂ by the H₂ reduction process with high methanol selectivity.

Methanol synthesis via CO2 hydrogenation over CuO–ZrO2 prepared by two-nozzle flame spray pyrolysis

Controlled CuO–ZrO₂ particle synthesis by tuning the flame spray pyrolysis conditions allow generating highly active and methanol selective CO₂ hydrogenation catalysts.

Recent progress in improving the stability of copper-based catalysts for hydrogenation of carbon–oxygen bonds

Five different strategies to enhance the stability of Cu-based catalysts for hydrogenation of C–O bonds are summarized in this review.

Bimetallic catalysts for green methanol production via CO2 and renewable hydrogen: a mini-review and prospects

This mini review discusses the recent advancements in the use of bimetallic catalysts for green methanol production via CO₂ hydrogenation.

A highly selective and stable ZnO-ZrO2 solid solution catalyst for CO2 hydrogenation to methanol

Although methanol synthesis via CO hydrogenation has been industrialized, CO₂ hydrogenation to methanol still confronts great obstacles of low methanol selectivity and poor stability, particularly for supported metal catalysts under industrial conditions. We report a binary metal oxide, ZnO-ZrO₂ solid solution catalyst, which can achieve methanol selectivity of up to 86 to 91% with CO₂ single-pass conversion of more than 10% under reaction conditions of 5.0 MPa, 24,000 ml/(g hour), H₂/CO₂ = 3:1 to 4:1, 320° to 315°C. Experimental and theoretical results indicate that the synergetic effect between Zn and Zr sites results in the excellent performance. The ZnO-ZrO₂ solid solution catalyst shows high stability for at least 500 hours on stream and is also resistant to sintering at higher temperatures. Moreover, no deactivation is observed in the presence of 50 ppm SO₂ or H₂S in the reaction stream.

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.