Cu/SiO2 catalysts prepared by the ammonia-evaporation method: Texture, structure, and catalytic performance in hydrogenation of dimethyl oxalate to ethylene glycol

Highly Effective Pd/MgO/γ-Al2O3 Catalysts for CO Oxidative Coupling to Dimethyl Oxalate: The Effect of MgO Coating on γ-Al2O3

The support of MgO/γ-Al₂O₃ was initially prepared by a multiple impregnation method and Pd was placed on the surface of the MgO/γ-Al₂O₃ support via incipient wetness impregnation. Pd/MgO/γ-Al₂O₃ (Pd/MAO) catalysts were systematically characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), CO₂-temperature-programmed desorption (TPD), transmission electron microscopy (TEM), CO-Fourier transform infrared (CO-FTIR), and X-ray photoelectron spectroscopy (XPS) and tested in the CO oxidative coupling to dimethyl oxalate (DMO) reaction. Compared to Pd/γ-Al₂O₃, the catalytic activities of the Pd/MAO catalysts improved significantly. The Pd/MAO catalyst with a 30% mass ratio of Mg to γ-Al₂O₃ delivers 3 times higher STY of DMO than that of Pd/γ-Al₂O₃. It has been demonstrated that MgO covered γ-Al₂O₃ layer-by-layer forming MAO supports, which can increase surface basicity and the interaction between Pd particles and the MAO supports. Moreover, the relationship between metal and support interaction and catalytic performance was discussed.

Ti3+ Tuning the Ratio of Cu+ /Cu0 in the Ultrafine Cu Nanoparticles for Boosting the Hydrogenation Reaction

Hydrogenation of diesters to diols is a vital process for chemical industry. The inexpensive Cu⁺ /Cu⁰ -based catalysts are highly active for the hydrogenation of esters, however, how to efficiently tune the ratio of Cu⁺ /Cu⁰ and stabilize the Cu⁺ is a great challenge. In this work, it is demonstrated that doped Ti ions can tune the ratio of Cu⁺ /Cu⁰ and stabilize the Cu⁺ by the TiOCu bonds in Ti-doped SiO₂ supported Cu nanoparticle (Cu/Ti-SiO₂ ) catalysts for the high conversion of dimethyl adipate to 1,6-hexanediol. In the synthesis of the catalysts, the Ti⁴⁺ OCu²⁺ bonds promote the reduction of Cu²⁺ to Cu⁺ by forming Ti³⁺ O_V Cu⁺ (O_V : oxygen vacancy) bonds and the amount of Ti doping can tune the ratio of Cu⁺ /Cu⁰ . In the catalytic reaction, the O vacancy activates CO in the ester by forming new Ti^{3+ δ} O_R Cu^{1+ δ} bonds (O_R : reactant oxygen), and Cu⁰ activates hydrogen. After the products are desorbed, the Ti^{3+ δ} O_R Cu^{1+ δ} bonds return to the initial state of Ti³⁺ O_V Cu⁺ bonds. The reversible TiOCu bonds greatly improve the activity and stability of the Cu/Ti-SiO₂ catalysts. When the content of Ti is controlled at 0.4 wt%, the conversion and selectivity can reach 100% and 98.8%, respectively, and remain stable for 260 h without performance degradation.

Deposition of Cubic Copper Nanoparticles on Silicon Laser-Induced Periodic Surface Structures via Reactive Laser Ablation in Liquid

We report the deposition of cubic copper nanoparticles (Cu NPs) of varying size and particle density on silicon laser-induced periodic surface structures via reactive laser ablation in liquid (RLAL) using intense femtosecond laser pulses. Two syntheses were compared: (1) simultaneous deposition, wherein a silicon wafer was laser-processed in aqueous Cu(NO₃)₂ solution and (2) sequential deposition, wherein the silicon wafer was laser-processed in water and then exposed to aqueous Cu(NO₃)₂. Only simultaneous deposition resulted in high Cu loading and cubic Cu NPs deposited on the surface. The solution pH, Cu(NO₃)₂ concentration, and sample translation rate were varied to determine their effects on the size, morphology, and density of Cu NPs. Solution pH near ∼6.8 maximized Cu deposition. The Cu(NO₃)₂ concentration affected the Cu NP morphology but not the size or Cu loading. The sample translation rate most significantly affected the Cu loading, particle size, and particle density. The observed synthesis parameter dependence of these Cu NP properties resembles results by electrodeposition to grow Cu NPs on silicon surfaces, which suggests that Cu NP deposition by RLAL follows a mechanism similar to electrodeposition.

Robust nickel silicate catalysts with high Ni loading for CO2 methanation

CO₂ is the main component of greenhouse gases and also an important carbon source. The hydrogenation of CO₂ to methane using Ni-based catalysts can not only alleviate CO₂ emissions but also obtain useful fuels. However, Ni-based catalysts face one major problem of the sintering of Ni nanoparticles in the process of CO₂ methanation. Thus, this work has synthesized a series of efficient and robust nickel silicate catalysts (NiPS-X) with different nickel content derived from nickel phyllosilicate by the hydrothermal method. It was found that the Ni loading plays a critical role in the structure and catalytic performance of the NiPS-X catalysts. The catalytic performance gradually increases with the increase of Ni loading. In particular, the highly dispersed NiPS-1.6 catalyst with a high Ni loading of 34.3 wt% could obtain the CO₂ conversion greater than 80%, and the methane selectivity was close to 100% for 48 h at 330 °C and the GHSV of 40,000 mL g^-1  h^-1 . The excellent catalytic property can be assigned to the high dispersion of Ni nanoparticles and the strong interaction between the active component and the carrier, which is derived from a unique layered silicate structure with lots of nickel phyllosilicate and a large number of Lewis acid sites.

Copper Phyllosilicates-Derived Catalysts in the Production of Alcohols from Hydrogenation of Carboxylates, Carboxylic Acids, Carbonates, Formyls, and CO2: A Review

Copper phyllosilicates-derived catalysts (CuPS-cats) have been intensively explored in the past two decades due to their promising activity in carbonyls hydrogenation. However, CuPS-cats have not been completely reviewed. This paper focuses on the aspects concerning CuPS-cats from synthesis methods, effects of preparation conditions, and dopant to catalytic applications of CuPS-cats. The applications of CuPS-cats include the hydrogenation of carboxylates, carboxylic acids, carbonates, formyls, and CO2 to their respective alcohols. Besides, important factors such as the Cu dispersion, Cu+ and Cu0 surface areas, particles size, interaction between Cu and supports and dopants, morphologies, and spatial effect on catalytic performance of CuPS-cats are discussed. The deactivation and remedial actions to improve the stability of CuPS-cats are summarized. It ends up with the challenges and prospective by using this type of catalyst.

Metal-Loaded Mesoporous MCM-41 for the Catalytic Wet Peroxide Oxidation (CWPO) of Acetaminophen

MCM-41 based catalysts (molar ratio Si/Al = 40) were prepared by a hydrothermal route, modified by ionic exchange with different metals (Cu, Cr, Fe and Zn) and finally calcined at 550 °C. The catalysts were fully characterized by different techniques that confirmed the formation of oxides of the different metals on the surfaces of all materials. Low-angle X-ray diffraction (XRD) analyses showed that calcination resulted in the incorporation of metallic Zn, Fe and Cr in the framework of MCM-41, while in the case of Cu, thin layers of CuO were formed on the surface of MCM-41. The solids obtained were tested in the catalytic wet peroxide oxidation (CWPO) of acetaminophen at different temperatures (25–55 °C). The activity followed the order: Cr/MCM-41 ≥ Fe/MCM-41 > Cu/MCM-41 > Zn/MCM-41. The increase of the reaction temperature improved the performance and activity of Cr/MCM-41 and Fe/MCM-41 catalysts, which achieved complete conversion of acetaminophen in short reaction times (15 min in the case of Cr/MCM-41). Fe/MCM-41 and Cr/MCM-41 were submitted to long-term experiments, being the Fe/MCM-41 catalyst the most stable with a very low metal leaching. The leaching results were better than those previously reported in the literature, confirming the high stability of Fe/MCM-41 catalysts synthesized in this study.

Hydrogenation of dimethyl oxalate to ethylene glycol over Cu/KIT-6 catalysts

Copper supported on KIT-6 mesoporous silica was prepared via ammonia evaporation (AE) method and applied for the catalytic hydrogenation of dimethyl oxalate (DMO) to ethylene glycol (EG).

Positive effects of a halloysite-supported Cu/Co catalyst fabricated by a urea-driven deposition precipitation method on the CO-SCR reaction and SO2 poisoning

Cu/Co catalysts were prepared on halloysite nanotube supports by a urea-driven deposition–precipitation method for CO oxidation and the selective catalytic reduction of NO (CO-SCR).

Influence of La-doping on the CuO/ZrO2 catalysts with different Cu contents for hydrogenation of dimethyl oxalate to ethylene glycol

The introduction of La2O3 into CuO/ZrO2 affects both the distribution of Cu species and the crystal growth of zirconia, hence increasing DMO conversion.

Tuning the Cu+ species of Cu-based catalysts for direct synthesis of ethanol from syngas

(1) Controllable Cu+–Cu0 sites were obtained by synthesizing xCu/yCuPS catalysts. (2) The outstanding catalytic activity was attributed to the balanced Cu+/(Cu+ + Cu0) (about 0.62). (3) The apparent catalytic activity was strongly related to Cu+.

The effect of supports on hydrogenation and water-tolerance of copper-based catalysts

Suitable interactions and the formation of Cu–M_xO_y interfaces could improve the water-tolerant hydrogenation properties of copper catalysts.

Promotional effect of indium on Cu/SiO2 catalysts for the hydrogenation of dimethyl oxalate to ethylene glycol

CuIn/SiO2 with 1.0 wt% indium shows the best catalytic performance for DMO hydrogenation to EG. The synergistic effect of Cu0–Cu+–CuIn alloy in activating H2 molecules and carbonyl bonds is elucidated.

Effects of precipitants on the catalytic performance of Cu/CeO2 catalysts for the water–gas shift reaction

The ratio of the precipitant (K2CO3 : KOH) was confirmed to affect the Cu dispersion and OSC of the Cu/CeO2 catalyst, and the Cu/CeO2 catalyst prepared with the K2CO3 : KOH ratio of 3 : 1 showed the highest activity.

Recent progress in hydrogenation of esters on heterogeneous bimetallic catalysts

The development and research of highly effective heterogeneous catalysts for the hydrogenation of esters, providing high activity and selectivity of the formation of the corresponding alcohols, is an urgent task of modern heterogeneous catalysis.

Hydrophobic Copper Catalysts Derived from Copper Phyllosilicates in the Hydrogenation of Levulinic Acid to γ-Valerolactone

A reduction-silylation-reduction method was developed to synthesize hydrophobic Cu catalysts derived from Cu phyllosilicates (CuPS). Triethoxy(octyl)silane (OTS) was used as the coupling agent. The OTS-grafted, reduced CuPS catalysts were applied in the hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL). The most promising catalyst was synthesized by reducing CuPS at a high temperature (350 °C for 3 h), followed by OTS grafting, and then by repeating the previous reduction step. High LA conversion (95.7%), GVL yield (85.2%), and stability (3 cycles with a 7.5% loss of initial activity) were obtained at a mild reaction condition (130 °C with a H₂ pressure of 12 bar). A high reduction temperature not only leads to a low oxidation state of Cu species but also suppresses the formation of silylation-induced acids. Moreover, the intrinsic activity of a reduced CuPS catalyst was nearly intact after subjecting to silylation and the second reduction treatment.

Enhanced Ethylene Glycol Selectivity of CuO-La2O3/ZrO2 Catalyst: The Role of Calcination Temperatures

The CuO-La₂O₃/ZrO₂ catalysts calcined at different temperatures from 500 to 800 °C were studied for the hydrogenation of oxalates to ethylene glycol (EG). Along with the increase of calcination temperatures, the BET surface area, pore volume, and Cu dispersion decreased, whereas the crystallite sizes of Cu species increased. Interestingly, the superior performance such as a 98% selectivity of EG in dimethyl oxalate hydrogenation or a 96.5% selectivity of EG in diethyl oxalate hydrogenation was obtained over the catalyst calcined at 700 °C. Essentially, the surface synergism between Cu species and monoclinic ZrO₂ was enhanced by the higher calcination temperature, resulting in the remarkable surface adsorption and activation of H₂. Besides, the increase of calcination temperature significantly reduced the surface acidity and basicity, which could effectively suppress the byproduct formation.

Catalytic Performances of Cu/MCM-22 Zeolites with Different Cu Loadings in NH3-SCR

The NH₃-SCR activities and hydrothermal stabilities of five xCu/MCM-22 zeolites with different Cu loadings (x = 2–10 wt%) prepared by incipient wetness impregnation method were systematically investigated. The physicochemical properties of xCu/MCM-22 zeolites were analyzed by XRD, nitrogen physisorption, ICP-AES, SEM, NH₃-TPD, UV-vis, H₂-TPR and XPS experiments. The Cu species existing in xCu/MCM-22 are mainly isolated Cu²⁺, CuO_x and unreducible copper species. The concentrations of both isolated Cu²⁺ and CuO_x species in xCu/MCM-22 increase with Cu contents, but the increment of CuO_x species is more distinct, especially in high Cu loadings (>4 wt%). NH₃-SCR experimental results demonstrated that the activity of xCu/MCM-22 is sensitive to Cu content at low Cu loadings (≤4 wt%). When the Cu loading exceeds 4 wt%, the NH₃-SCR activity of xCu/MCM-22 is irrelevant to Cu content due to the severe pore blockage effects caused by aggregated CuO_x species. Among the five xCu/MCM-22 zeolites, 4Cu/MCM-22 with moderate Cu content has the best NH₃-SCR performance, which displays higher than 80% NO_x conversions in a wide temperature window (160–430 °C). Furthermore, the hydrothermal aging experiments (xCu/MCM-22 was treated at 750 °C for 10 h under 10% water vapor atmosphere) illustrated that all the xCu/MCM-22 zeolites exhibit high hydrothermal stability in NH₃-SCR reactions.

Combustion Products of Calcium Carbide Reused by Cu-Based Catalysts for Acetylene Carbonylation

Sustainable development is a worldwide concern. This work mainly focuses on the reuse of the combustion products of calcium carbide and the influence of different kinds of copper on the acetylene carbonylation reaction. A series of catalysts were prepared by heating the precursors under various atmospheres (air, hydrogen, and nitrogen). The X-ray diffraction and the X-ray photoelectron spectroscopy have been analyzed regarding copper species composition and content in catalysts. The result of the Cu⁺-promoted reaction was in good agreement with the conducted density functional theory analysis, and we speculate that Cu⁺ promotes the transfer of electrons in the reaction. Transmission electron microscopy and elemental mapping evaluation confirmed the difference in Cu dispersion. Characterization of catalysts using temperature programmed desorption and pyridine Fourier-transform infrared revealed differences in their acidity. Acidity was found to be favorable for acetylene carbonylation. Selectivity and yield of the CuAlZn-LDO(N) catalyst at 225 °C were 73 and 70%, respectively, and the catalyst showed good stability over two consecutive cycles of reuse.

CO direct esterification to dimethyl oxalate and dimethyl carbonate: the key functional motifs for catalytic selectivity

The direct esterification of CO involves processes using CO as the starting material and ester chemicals as products. Dimethyl oxalate (DMO) and dimethyl carbonate (DMC) are two different products of the direct CO esterification reaction. However, the effective control of the reaction pathway and direct synthesis of DMO and DMC are challenging. In this review, we summarize the recent research progress on the direct esterification of CO to DMO/DMC and reveal the functional motifs responsible for the catalytic selectivity. Firstly, we discuss the microstructure of catalysts for the direct esterification of CO to DMO and DMC, including the valence state and the aggregate state of Pd. Then, the influence of characteristics of the support on the selectivity is analyzed. Importantly, the aggregate state of the active component, Pd is deemed as a vital functional motif for catalytic selectivity. The isolated Pd is conducive for the formation of DMC, while the aggregated Pd is beneficial for the formation of DMO. This review will provide rational guidance for the direct esterification of CO to DMO and DMC.

Cu-Promoted Iron Catalysts Supported on Nanorod-Structured Mn-Ce Mixed Oxides for Higher Alcohol Synthesis from Syngas

A series of supports were prepared through the method of hydrothermal synthesis, and copper–iron catalysts supported on ceria nanorods modified by different amounts of manganese were prepared by the liquid phase co-reduction method. The effect of the catalytic performance after Mn addition mainly on higher alcohols synthesis (HAS) was evaluated. Different techniques, such as BET, ICP-AES, XRD, H2-TPR, CO-TPD, TEM, FESEM, XPS and MES, were performed for catalyst characterization. The results indicated that the abilities of CO chemical desorption and carbon chain growth were promoted with appropriate Mn addition, and higher ratio of Cu0/Cu+ species facilitated the methanol homologous reaction and the C2+OH formation. The Ce4+ species were reduced into Ce3+ species during HAS process, providing a large amount of oxygen vacancies. Proper Mn content promoted the formation of χ-Fe5C2 and leaded to the Fe 2p binding energy shift, causing the electron transformation between Fe and Mn species. The largest weight selectivity of C2+OH appeared in the reaction over CuFe/3.6MnCe catalyst with CO conversion 41.43%, and weight fraction of C2+OH 84.41 wt% in the alcohols distribution.