In Situ Fourier Transform Infrared Investigation on the Low-Level Carbon Dioxide Conversion over a Nickel/Titanium Dioxide Catalyst

Efficiently converting atmospheric carbon dioxide (CO2) is crucial for sustainable human development. In this study, we conducted systematic in situ Fourier transform infrared tests to examine how hydrogen (H2) partial pressure affects the conversion of low-level CO2 (around 400 ppm) using nickel/titanium dioxide (Ni/TiO2). Results show that increasing H2 partial pressure significantly increases surface monodentate formate species, leading to enhanced methane (CH4) production at both 250 and 400 °C. Conversely, on Ni's surface, the key species are formyls and bidentate formate at 250 °C, but these decrease significantly at 400 °C. These findings indicate that low-level CO2 is more easily converted to CH4 over Ni/TiO2 than Ni, regardless of temperature. Additionally, the strong Ni-TiO2 interaction gives Ni/TiO2 an advantage in converting low CO2 concentrations, with excellent durability even at 400 °C. This study enhances our understanding of direct CO2 conversion and aids in the development of advanced CO2 emission reduction technologies.

UiO-66 MOF-Derived Ru@ZrO2 Catalysts for Photo-Thermal CO2 Hydrogenation

The use of metal–organic frameworks (MOFs) as templates or precursors in the manufacture of heterogeneous catalysts is highly attractive due to the transfer of MOFs’ inherent porosity and homogeneous metallic distribution to the derived structure. Herein, we report on the preparation of MOF-derived Ru@ZrO2 catalysts by controlled thermal treatment of zirconium-based MOF UiO-66 with ruthenium moieties. Ru3+ (3 or 10 mol%) precursor was added to UiO-66 synthesis and, subsequently, the as-synthesized hybrid structure was calcined in flowing air at different temperatures (400–600 °C) to obtain ZrO2-derived oxides doped with highly dispersed Ru metallic clusters. The materials were tested for the catalytic photo-thermal conversion of CO2 to CH4. Methanation experiments were conducted in a continuous flow (feed flow rate of 5 sccm and 1:4 CO2 to H2 molar ratio) reactor at temperatures from 80 to 300 °C. Ru0.10@ZrO2 catalyst calcined at 600 °C was able to hydrogenate CO2 to CH4 with production rates up to 65 mmolCH4·gcat.–1·h–1, CH4 yield of 80% and nearly 100% selectivity at 300 °C. The effect of the illumination was investigated with this catalyst using a high-power visible LED. A CO2 conversion enhancement from 18% to 38% was measured when 24 sun of visible LED radiation was applied, mainly due to the increase in the temperature as a result of the efficient absorption of the radiation received. MOF-derived Ru@ZrO2 catalysts have resulted to be noticeably active materials for the photo-thermal hydrogenation of CO2 for the purpose of the production of carbon-neutral methane. A remarkable effect of the ZrO2 crystalline phase on the CH4 selectivity has been found, with monoclinic zirconia being much more selective to CH4 than its cubic allotrope.

CO2 Methanation over Nickel Catalysts: Support Effects Investigated through Specific Activity and Operando IR Spectroscopy Measurements

Renewed interest in CO2 methanation is due to its role within the framework of the Power-to-Methane processes. While the use of nickel-based catalysts for CO2 methanation is well stablished, the support is being subjected to thorough research due to its complex effects. The objective of this work was the study of the influence of the support with a series of catalysts supported on alumina, ceria, ceria–zirconia, and titania. Catalysts’ performance has been kinetically and spectroscopically evaluated over a wide range of temperatures (150–500 °C). The main results have shown remarkable differences among the catalysts as concerns Ni dispersion, metallic precursor reducibility, basic properties, and catalytic activity. Operando infrared spectroscopy measurements have evidenced the presence of almost the same type of adsorbed species during the course of the reaction, but with different relative intensities. The results indicate that using as support of Ni a reducible metal oxide that is capable of developing the basicity associated with medium-strength basic sites and a suitable balance between metallic sites and centers linked to the support leads to high CO2 methanation activity. In addition, the results obtained by operando FTIR spectroscopy suggest that CO2 methanation follows the formate pathway over the catalysts under consideration.

Metal Nanoclusters Synthesized in Alkaline Ethylene Glycol: Mechanism and Application

The "unprotected" metal and alloy nanoclusters (UMCs) prepared by the alkaline ethylene glycol method, which are stabilized with simple ions and solvent molecules, have the advantages of a small particle size, a narrow size distribution, good stability, highly efficient preparation, easy separation, surface modification and transfer between different phases. They can be composited with diverse materials to prepare catalytic systems with controllable structures, providing an effective means of studying the different factors' effects on the catalytic properties separately. UMCs have been widely used in the development of high-performance catalysts for a variety of functional systems. This paper will review the research progress on the formation mechanism of the unprotected metal nanoclusters, exploring the structure-function relationship of metal nanocluster catalysts and the preparation of excellent metal catalysts using the unprotected metal nanoclusters as building blocks or starting materials. A principle of the influence of carriers, ligands and modifiers in metal nanocluster catalysts on the catalytic properties is proposed.

Promotion of Ru or Ni on Alumina Catalysts with a Basic Metal for CO2 Hydrogenation: Effect of the Type of Metal (Na, K, Ba)

Ru and Ni on alumina catalysts have been promoted with a 10 wt% of alkali metal (K or Na) or alkaline earth metal (Ba) and tested in CO₂ methanation. For the catalyst consisting of Ni and Ba, the variation of Ba loading while keeping Ni loading constant was studied. The promotion in terms of enhanced CH₄ yield was found only for the addition of barium to 15 wt% Ni/Al₂O₃. In contrast, K and Na addition increased the selectivity to CO while decreasing conversion. For the Ru-based catalyst series, no enhancement in conversion or CH₄ yield was attained by any of the alkaline metals. CO₂ temperature-programed desorption (CO₂-TPD) revealed that the amount of chemisorbed CO₂ increased significantly after the addition of the base metal. The reactivity of CO_x ad-species for each catalyst was assessed by temperature-programed surface reaction (TPSR). The characterization revealed that the performance in the Sabatier reaction was a result of the interplay between the amount of chemisorbed CO₂ and the reactivity of the COx ad-species, which was maximized for the (10%Ba)15%Ni/Al₂O₃ catalyst.

Hydrogen reverse spillover eliminating methanation over efficient Pt–Ni catalysts for the water–gas shift reaction

Hydrogen reverse spillover from Ni0 sites to Pt sites completely eliminated the side reaction of methanation and improved the catalytic activity of Ni0 sites over a nickel phyllosilicate-supported Pt–Ni catalyst during the water–gas shift reaction.