Carbon dioxide hydrogenation to methanol over multi-functional catalyst: Effects of reactants adsorption and metal-oxide(s) interfacial area

Infrared photodissociation spectroscopy of mass-selected [TaO3(CO2)n]+ (n = 2-5) complexes in the gas phase

We report a joint experimental and theoretical study on the structures of gas-phase [TaO₃(CO₂)_n]⁺ (n = 2-5) ion-molecule complexes. Infrared photodissociation spectra of mass-selected [TaO₃(CO₂)_n]⁺ complexes were recorded in the frequency region from 2200 to 2450 cm^-1 and assigned through comparing with the simulated infrared spectra of energetically low-lying structures derived from quantum chemical calculations. With the increasing number of attached CO₂ molecules, the larger clusters show significantly enhanced fragmentation efficiency and a strong band appears at around 2350 cm^-1 near the free CO₂ antisymmetric stretching vibration band, indicating only a small perturbation of CO₂ molecules on the secondary solvation sphere while higher frequency bands corresponding to the core structure remain largely unaffected. A core structure [TaO₃(CO₂)₃]⁺ is identified to which subsequent CO₂ ligands are weakly attached and the most favorable cluster growth path is verified to proceed on the triplet potential energy surface higher in energy than that of ground states. Theoretical exploration reveals a two-state reactivity (TSR) scenario in which the energetically favored triplet transition state crosses over the singlet ground state to form a TaO₃⁺ core ion, providing new information on the cluster formation correlated with the reactivity of tantalum metal oxides towards CO₂.

Manganese Oxide as a Promoter for Copper Catalysts in CO2 and CO Hydrogenation

In this work, we discuss the role of manganese oxide as a promoter in Cu catalysts supported on graphitic carbon during hydrogenation of CO2 and CO. MnOx is a selectivity modifier in an H2/CO2 feed and is a highly effective activity promoter in an H2/CO feed. Interestingly, the presence of MnOx suppresses the methanol formation from CO2 (TOF of 0.7 ⋅ 10-3 s-1 at 533 K and 40 bar) and enhances the low-temperature reverse water-gas shift reaction (TOF of 5.7 ⋅ 10-3 s-1) with a selectivity to CO of 87 %C. Using time-resolved XAS at high temperatures and pressures, we find significant absorption of CO2 to the MnO, which is reversed if CO2 is removed from the feed. This work reveals fundamental differences in the promoting effect of MnOx and ZnOx and contributes to a better understanding of the role of reducible oxide promoters in Cu-based hydrogenation catalysts.

Electroplating sludge-derived metal and sulfur co-doping catalyst and its application in methanol production by CO2 catalytic hydrogenation

Electroplating sludge is a hazardous waste and its recycling is a hot topic. Electroplating sludge usually contains plenty of transition metals and multi-hetero atoms, which are potential resources. For the first time, this work synthesized spinel catalyst from Zn- and Cr-containing electroplating sludges by a simple calcination method, and applied the obtained catalysts in CH₃OH production by CO₂ catalytic hydrogenation. The spinel was doped by various heteroatoms, including Fe, Mn, Cu, and even S. According to detailed characterizations, the metal doping increased the low-temperature conversion efficiency of CO₂ but decreased the CH₃OH selectivity at the same time. After a further doping of S, although CO₂ conversion efficiency was slightly decreased, the selectivity of CH₃OH was significantly increased. After all, the optimized catalyst attained a conversion efficiency of 8.6% (CO₂) as well as a selectivity of 73.3% (CH₃OH) at 250 °C and 3 MPa. As a result, above results realized high-value-added utilization of hazardous waste and producing valuable product at the same time, which was in favor of circular development.

Co-Production of Methanol and Methyl Formate via Catalytic Hydrogenation of CO2 over Promoted Cu/ZnO Catalyst Supported on Al2O3 and SBA-15

Cu/ZnO catalysts promoted with Mn, Nb and Zr, in a 1:1:1 ration, and supported on Al2O3 (CZMNZA) and SBA-15 (CZMNZS) were synthesized using an impregnation method. The catalytic performance of methanol synthesis from CO2 hydrogenation was investigated in a fixed-bed reactor at 250 °C, 22.5 bar, GHSV 10,800 mL/g·h and H2/CO2 ratio of 3. The CZMNZA catalyst resulted in higher CO2 conversion and MeOH selectivity of 7.22% and 32.10%, respectively, despite having a lower BET surface area and pore volume compared to CZMNZS. Methyl formate is the major product obtained over both types of catalysts. The CZMNZA is a promising catalyst for co-producing methanol and methyl formate via the CO2 hydrogenation reaction.

Effects of Promoter’s Composition on the Physicochemical Properties of Cu/ZnO/Al2O3-ZrO2 Catalyst

Cu/ZnO catalysts were synthesized via an impregnation method on an Al2O3-ZrO2 support and modified by the addition of manganese and niobium as promoters. The effect of the selected promoters on the physicochemical properties and performance toward the hydrogenation of CO2 to methanol are presented in this paper. The Mn and Nb promoters improved the reducibility of the catalyst as evidenced by the shifting of the H2-TPR peaks from 315 °C for the un-promoted catalyst to 284 °C for the Mn- and Nb-promoted catalyst. The catalytic performance in a CO2 hydrogenation reaction was evaluated in a fixed-bed reactor system at 22.5 bar and 250 °C for 5 h. Amongst the catalysts investigated, the catalyst with equal ratio of Mn and Nb promoters exhibited the smallest particle size of 6.7 nm and highest amount of medium-strength basic sites (87 µmol/g), which resulted in the highest CO2 conversion (15.9%) and methanol selectivity (68.8%).

Silica-Related Catalysts for CO2 Transformation into Methanol and Dimethyl Ether

The climate situation that the planet is experiencing, mainly due to the emission of greenhouse gases, poses great challenges to mitigate it. Since CO2 is the most abundant greenhouse gas, it is essential to reduce its emissions or, failing that, to use it to obtain chemicals of industrial interest. In recent years, much research have focused on the use of CO2 to obtain methanol, which is a raw material for the synthesis of several important chemicals, and dimethyl ether, which is advertised as the cleanest and highest efficiency diesel substitute fuel. Given that the bibliography on these catalytic reactions is already beginning to be extensive, and due to the great variety of catalysts studied by the different research groups, this review aims to expose the most important catalytic characteristics to take into account in the design of silica-based catalysts for the conversion of carbon dioxide to methanol and dimethyl ether.

New Hydrogen-Bond-Enriched 1,3,5-Tris(2-hydroxyethyl) Isocyanurate Covalently Functionalized MCM-41: An Efficient and Recoverable Hybrid Catalyst for Convenient Synthesis of Acridinedione Derivatives

A new nano-ordered 1,3,5-tris(2-hydroxyethyl) isocyanurate-1,3-propylene covalently functionalized MCM-41 (MCM-41-Pr-THEIC) was designed and prepared at room temperature through a simple procedure. According to various microscopic, spectroscopic, or thermal methods and techniques, the correlation of the catalytic performance of the hybrid mesoporous MCM-41-Pr-THEIC to its structural characteristics was fully confirmed. The new MCM-41-Pr-THEIC organosilica nanomaterials were successfully investigated as a solid mild nanocatalyst through hydrogen-bonding activation provided by its organic moiety, for the pseudo-four-component condensation of dimedone, aldehydes, and ammonium acetate or p-toluidine to afford the corresponding acridinedione derivatives under green conditions. Furthermore, the introduced nanocatalyst could be reused at least four times with negligible loss of its activity, indicating the good stability and high activity of the new hybrid organosilica.