Solid Solution Catalysts Research Articles

The atom-efficient production of glycerol carbonate via transesterification between dimethyl carbonate and glycerol over fluorinated Al2O3-ZrO2 solid solution catalysts with suitable acidic-basic property

A series of Al2O3-ZrO2-nF solid solution catalysts (n was the F: Al atomic ratios) with Al: Zr molar ratio of 0.2, was fabricated by addition of varied amounts of (AlF6)3- into the ZrO2 via a co-precipitation method. To our delight, the acidic-basic properties of Al2O3-ZrO2-nF can be tuned by the change of n. Then, the role of acidic-basic sites was investigated for the glycerol carbonate (GLC) production from glycerol and dimethyl carbonate (DMC). Despite that the more basic samples exhibited higher reactivities compared to that of the more acidic ones, the cooperative effect between the acidic-basic pairs can enhance the catalyst activity strongly. So, the catalyst with F/Al= 1.0 can realize the quantitative and selective transformation of glycerol to GLC applying DMC/glycerol of 1:1 ratio with a GLC yield of 91.2%, owing to its appropriate acidic-basic property. Furthermore, the uniform solid solution structure can prevent the generation of free Al or F species, assuring the catalytic material an excellent stability. More importantly, several green parameters including process mass intensity, environmental factor and atom utilization were calculated to confirm the environmental and economic compatibility of the GLC synthesis over the model catalyst.

Enhanced Diclofenac Photomineralization under Solar Light Using Ce1−xZnxO2−x Solid Solution Catalysts: Synergistic Effect of Photoexcited Electrons and Oxygen Vacancies

The present work describes the synthesis, characterization, and photomineralization activity of synthesized Ce1−xZnxO2−x solid solution catalysts allowing the degradation of diclofenac as a model of anti-inflammatory medicines in water. The oxygen-deficient photocatalyst Ce1−xZnxO2−x (CeZnx), produced by mixing ZnO and CeO2, is characterized for its crystallographic parameters, specific surface area, and morphology. Photomineralization activity determination using TOC analysis shows efficient diclofenac photo-oxidation under sunlight. Moreover, the results indicate that the coexistence of Zn2+ and Ce4+ and the oxygen vacancies rate in CeZnx solid solution are key factors for strong drug mineralization. Ultimately, CeZn0.1, which is one of the photocatalysts synthesized in the present work, represents a cheap and efficient reagent for organic matter photomineralization in wastewater.

Hydrogenation of Carbon Dioxide to Methanol over Non-Noble Catalysts: A State-of-the-Art Review

The malignant environmental changes caused by the ever-increasing amount of anthropogenic CO2 emissions have been particularly prominent in recent years. To achieve carbon mitigation and carbon neutrality, CO2 hydrogenation to methanol is regarded as a promising and sustainable route. However, the development of catalysts with exceptional performance and the establishment of a clear structure–activity relationship remain formidable challenges. Considering the lack of a state-of-the-art review on the catalytic progress of CO2 hydrogenation to methanol over non-noble catalysts, we conducted a detailed review in terms of the thermodynamic analysis, catalytic development, and reaction mechanism. In this work, we mainly reviewed the latest research progress of different catalysts including Cu-based, In2O3-based, bimetallic, solid solution, and other catalysts. Meanwhile, we summarized the effects of the support materials, promoters, and preparation methods on the catalytic performance. In addition, we also summarized the possible reaction mechanisms of direct hydrogenation of CO2 to methanol. Overall, this work would be of importance for the researchers to obtain a comprehensive understanding of the design and development of efficient catalysts for CO2 hydrogenation to methanol.

Boosting total oxidation of methane over NiO nanocrystalline decorated ZnO-CoNi solid solution via photothermal synergism

In the context of global warming and atmospheric methane growth, photo-assisted total oxidation of methane is of great importance to diminish greenhouse effect. However, catalytic oxidation of methane at ambient conditions remains a formidable challenge because of its high structure stability. Herein, we report a highly active and stable NiO nanocrystalline decorated on ZnO-CoNi solid solution (NiO/ZnO-CoNi) catalyst which enables 88 % photocatalytic conversion of methane to CO2 and H2O under ambient conditions to maintain a continuous reaction. The unprecedented photocatalytic performance of NiO/ZnO-CoNi originates from the high mobility of surface lattice oxygen of supported NiO nanocrystallines driven by the photogenerated electrons and internal electric field of ZnO-CoNi solid solution. More importantly, the methane conversion of NiO/ZnO-CoNi remains higher than 37 % even when the methane concentration is up to 5000 ppm, showing promise for methane elimination applications in the vicinity of large methane emission sources.

Boosting catalytic activity of Cu-Ce solid solution catalysts by flame spray pyrolysis with high Cu+ concentration and oxygen vacancies

Cu-Ce solid solution catalysts are remarkable in catalytic oxidation. However, the traditional synthesis methods struggle to prevent severe phase separation at high Cu concentration. In this study, a stable Cu-Ce solid solution with a Cu content>30% was synthesized by flame spray pyrolysis (FSP). Flame synthesis process with a high reaction temperature of 2000 K and rapid cooling characteristics of over 100 K cm−1 resulted in the enrichment of Cu elements on the catalyst's surface as Cu+. The high Cu content fostered abundant surface oxygen vacancies on the catalyst. The catalyst surface has more CO activation sites due to the high Cu+ concentration, and the abundant oxygen vacancies bring greater oxygen activation ability to the catalyst. It was found that Cu-30 had a reaction rate of 0.48 μmolCO g−1 s−1 at 60 °C, dozens of times higher than other catalysts, and achieved complete conversion of CO at 120 °C. The mechanism suggests that the active site of CO is the surface Cu+, and the oxygen vacancies provide active oxygen species, which facilitate the CO catalytic reaction's rapid progress.

Ce doping promote the selective conversion of ethanol to ethyl acetate via the dehydrogenation-condensation over CuCeZr catalyst

Ethyl acetate, as an important organic solvent, can be produced via ethanol dehydrogenation-condensation route with 96% atomic economy and environmental friendliness. Although CuZr-based catalysts have been widely used in this reaction, high ethyl acetate selectivity with satisfied ethanol conversion remains a great challenge. Herein, an efficient CuCeZr solid solution catalyst is developed and realize the selective synthesis of ethyl acetate from ethanol. The CuCeZr catalyst with 10 wt% Ce doping shows the highest selectivity (87.5%) and 55.9% ethanol conversion, which is superior to other reported CuZr-based catalysts. A 1000 h continuous life-test result indicates an excellent stability of CuCeZr catalyst. The characterization and reaction results suggest that the Ce doping enhanced the formation of Cu (I) species to improve the selectivity of ethyl acetate. Moreover, it decreases the amount of strong acid-base sites, which suppresses the self-condensation of acetaldehyde and dehydration process, reducing the production of C4 by-products.

Room-Temperature Transient Hydrogen Uptake of MgH2 Induced by Nb-Doped TiO2 Solid-Solution Catalysts.

The practical applications of MgH2 as a high-density hydrogen carrier depend heavily on efficient and low-cost catalysts to accelerate the dehydriding/hydriding reactions at moderate temperatures. In the present work, this issue is addressed by synthesizing Nb-doped TiO2 solid-solution-type catalysts that dramatically improve the hydrogen sorption performances of MgH2. The catalyzed MgH2 can absorb 5 wt % of H2 even at room temperature for 20 s, release 6 wt % of H2 at 225 °C within 12 min, and the complete dehydrogenation can be achieved at 150 °C under a dynamic vacuum atmosphere. Density functional theory calculations reveal that Nb doping introduces Nb 4d orbitals with stronger interaction with H 1s into the density of states of TiO2. This considerably enhances both the adsorption and dissociation ability of the H2 molecule on the catalysts surface and the hydrogen diffusion across the specific Mg/Ti(Nb)O2 interface. The successful implementation of solid solution-type catalysts in MgH2 offers a demonstration and inspiration for the development of high-performance catalysts and solid-state hydrogen storage materials.

Light-driven CO2 methanation over Au-grafted Ce0.95Ru0.05O2 solid-solution catalysts with activities approaching the thermodynamic limit

Light-driven CO2 methanation over Au-grafted Ce0.95Ru0.05O2 solid-solution catalysts with activities approaching the thermodynamic limit

Copper-doped ZnO-ZrO2 solid solution catalysts for promoting methanol synthesis from CO2 hydrogenation.

Copper-doped ZnO-ZrO2 solid solution catalysts were synthesized via co-precipitation for promoting CH3OH synthesis via hydrogenation of CO2. Various testing methods were applied to investigate the effect of various copper contents on the catalysts. The catalytic performance was evaluated by a fixed bed reactor. XRD, HRTEM and Raman spectra collectively indicated that a ZnO-ZrO2 solid solution catalyst with 3% Cu had a higher Cu dispersion, while the H2-TPR results confirmed that a catalyst with 3% Cu had more Cu active sites under low temperature H2 pretreatment. When the copper content increased to 5% and 10%, the catalyst showed a better Cu crystallinity and a worse Cu dispersion, which could have a negative effect. Therefore, the CO2 conversion and methanol yield with a 3% CuZnO-ZrO2 catalyst at 5 MPa, 250°C and 12 000 ml/(g h) increased by 8.6% and 7.6%, respectively. Moreover, the CH3OH selectivity and catalytic stability of the solid solution catalyst were better than those of the traditional CZA catalyst.

Asymmetric Sites on the ZnZrOx Catalyst for Promoting Formate Formation and Transformation in CO2 Hydrogenation.

The role of formate species for CO2 hydrogenation is still under debate. Although formate has been frequently observed and commonly proposed as the possible intermediate, there is no definite evidence for the reaction of formate species for methanol production. Here, formate formation and conversion over the ZnZrOx solid solution catalyst are investigated by in situ/operando diffuse reflectance infrared Fourier transform spectroscopy-mass spectroscopy (DRIFTS-MS) coupled with density functional theory (DFT) calculations. Spectroscopic results show that bidentate carbonate formed from CO2 adsorption is hydrogenated to formate on Zn-O-Zr sites (asymmetric sites), where the Zn site is responsible for H2 activation and the Zr site is beneficial for the stabilization of reaction intermediates. The asymmetric Zn-O-Zr sites with adjacent and inequivalent features on the ZnZrOx catalyst promote not only formate formation but also its transformation. Both theoretical and experimental results demonstrate that the origin of the excellent performance of the ZnZrOx catalyst for methanol formation is associated with the H2 heterolytic cleavage promoted by the asymmetric Zn and Zr sites.

Boosting Conversion of CO2 to Light Olefins over MgO-Promoted ZnZrO/SAPO-34 Bifunctional Catalyst

CO2 hydrogenation to produce light olefins is a hopeful route to the cyclic utilization of CO2. Although metal oxide/zeolite bifunctional catalysts show outstanding performance for CO2 hydrogenation to olefins, they still expect to further improve its performance. Here, a ternary metal oxide solid solution catalyst by incorporating MgO into ZnZrO to adjust the acid and redox active sites and coupled with SAPO-34 zeolite (noted as Mg-ZnZrO/SAPO-34) was developed. The Mg-ZnZrO/SAPO-34 catalyst exhibits light olefins yield of 5.7% that higher than those of ZnZrO/SAPO-34 catalyst (4.5%) at 390 °C. The results discovered that the introduction of MgO can neutralize the strong acid site of zeolite and generate more oxygen vacancies, and exhibit superior ability to adsorb and activate CO2 and H2. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) demonstrate that carbonate formation by CO2 adsorption of doped MgO and participation in the reaction to form more HCOO* and CH3O* species on the Mg-ZnZrO/SAPO-34 catalyst. The strategy via adjusting the acid intensity and the content of oxygen vacancies developed in this work supplies a guideline to design high-performance catalysts for CO2 utilization.

Zn-CdZrOx solid solution catalysts for hydrogenation of CO2 to methanol

CO2 is one of the members of greenhouse gases, and its capture, collection, and recycling have aroused widespread concern. Methanol is not only a basic organic chemical raw material, but also a high-quality clean fuel. The idea of CO2 hydrogenation to methanol can turn waste into treasure and realize the resource utilization of CO2 ultimately. Of course, the value of solving environmental and energy problems is immeasurable.Here, a series of y% Zn-doped CdZrOx catalysts are prepared and the 5.0% Zn-CdZrOx shows 80.82% methanol selectivity and 8.52% CO2 conversion rate at 320℃. Combining HRTEM images and XRD patterns, it is found that 5% Zn-CdZrOx shows the structure of the solid solution. CO2-TPD shows that the desorption peak area of 5.0% Zn-CdZrOx is large, which means more beneficial to CO2 adsorption and activation. H2-TPR indicates the existence of the strongly synergistic interaction between Zn, Cd, and Zr of 5.0% Zn-CdZrOx. From the in-situ DRIFTS, the peaks of HCOO* and H3CO* species are monitored, which is important to methanol formation.It is supposed there is a synergistic effect between Cd, Zn, and Zr in this catalyst and the structure of the solid solution is the decisive factor for the activity of CO2 hydrogenation to methanol.

The high activity of Co-Mn-based solid solution catalysts for lean methane combustion

Developing non-noble metal-based catalysts for methane combustion with high catalytic activity and stability is important in the new context of a changing global energy landscape. In this study, we reported an Co5Mn1-O catalyst achieved 90% conversion of methane to CO2 at 305 °C, which was about 60 ℃ lower than the catalysts reported. The synthetic strategy via lattice distortion that inhibits the deep oxidation of Mn2+ with prepared a highly catalytic reactive Co-Mn-based solid solution material. The results show that introduction of Mn atoms into the Co3O4 spinel structure caused lattice distortion, which modulated the oxygen coordination environment and oxygen vacancies of the catalyst, and the Co5Mn1-O (Optimum) catalyst prepared under optimized conditions obtained excellent methane activation capacity and lattice oxygen mobility. The higher lattice oxygen mobility of the Co5Mn1-O catalyst facilitated the adsorption, activation, and oxidation of methane, especially the rate-determining step of methane oxidation, the conversion of CH4 to CH3-. The conversion rate decreases slightly in the presence of 5 vol% or 10 vol% H2O, but it also still maintained good catalytic activity and stability under high temperatures and long-term reactions. In addition, in situ infrared specra was used to explore the reaction mechanism of methane combustion under real reaction conditions.

Local electron-rich structures facilitating the efficient synthesis of dimethyl carbonate from propylene carbonate and methanol over a ZnO/ZrO2 solid solution catalyst

ZnO/ZrO2 solid solution was introduced as the catalyst for synthesizing dimethyl carbonate (DMC) from propylene carbonate (PC) and methanol. Homogeneous catalysts with strong alkaline nature are the current main catalysts for this reaction. Therefore, to supplant the former with a more applicable multiphase one, it is necessary to construct stable and efficient alkaline active centers on the surface of solid catalysts. The ZnO/ZrO2 solid solution created defective structures of coordinative unsaturation in the form of oxygen vacancies (OV) by substituting Zn atoms for Zr atoms in ZrO2 crystals. Characterizations showed that electrons were transferred to the surrounding Zn atoms upon the formation of these OV, leading to a local enrichment of electrons and the formation of basic active centers. The number of oxygen defects and the alkalinity were effectively regulated by changing the ratio of the two metal atoms in the solid solution. Experiments demonstrated that the catalyst had the best DMC selectivity (92.2%) and the highest DMC yield (57.2%) at a 1:1 ratio of Zn to Zr, at 160 °C and 4 h. This superior performance not only establishes the feasibility of solid solution catalysts in synthesizing DMC but also provides a new perspective on the essential understanding of the active centers of such catalysts.

Unraveling reactive oxygen species-dependent toluene mineralization routes via construction of TixSn1−xO2 infinite solid solution photocatalysts

Intermediates seriously affect the reaction process and rate in terms of kinetics. However, there are few studies on the effect of reactive oxygen species on intermediates of toluene mineralization. Herein, SnO2 and TixSn1−xO2 infinite solid solution photocatalysts are prepared and the mineralization ability of Ti0.1Sn0.9O2 is 2.7 times that of SnO2. Introduction of Ti shifts the conduction band position upward, providing thermodynamic possibility for superoxide radicals formation. The sole hydroxyl radicals over SnO2 lead to the generation of benzyl alcohol; while synergetic hydroxyl radicals and superoxide radicals result in benzoic acid existed in solid solution catalysts. Theoretical calculation confirms that benzoic acid has lower ring opening barrier, thereby improving toluene mineralization ability over TixSn1−xO2. The synergetic roles of Ti and Sn in adsorption and activation of water and toluene moleculars are also proposed. This work provides new insights into reactive oxygen radicals regulation to alter intermediates and ease toluene removal.

A Banana-like Ni-MgO Solid Solution Catalyst Derived from Bimetallic Ni-Mg@MOFs for Hydrogenation of Nitroarenes

: The design and synthesis of an efficient Ni-MgO solid solution catalyst with specific morphology for the hydrogenation of nitroarenes is highly required. In this work, a banana-like Ni-MgO solid solution incorporation of carbon catalyst (termed as Ni/MgO-C) has been synthesized via a MOFs-templating strategy for one-step pyrolysis of bimetallic Ni-Mg@MOFs. : The developed Ni/MgO-C catalyst was applied to the hydrogenation of nitroarenes reaction, which exhibited good performance for the hydrogenation of nitroarenes to the corresponding arylamines. : The Ni-Mg@MOFs served as a precursor for the preparation of a solid solution catalysts that could improve the dispersion of Ni species, reduce the size of metallic Ni, and strengthen the Ni-MgO interaction, enhance the transfer of electron density. All of these are beneficial for improving the performance of the hydrogenation process. : This MOFs-templating strategy may provide a facile method for the synthesis of Ni-MgO solid solution catalyst for other hydrogenation reactions.

The construction of nanotubular Ni-Mg phyllosilicate solid solution catalyst for boosting CO2 catalytic conversion: Identifying the species variations and interactions

Addressing the problems of easy collapse, Ni sintering and low catalytic activity over the nanotubular nickel phyllosilicate catalyst, the Mg species was doped via a simple hydrothermal method to construct the nanotubular Ni-Mg bimetallic phyllosilicate solid solution. The high thermal stability, nonreducible property and strong basicity of magnesium species led to the enhancement of anti-collapse, Ni-sintering resistance and basicity. As a result, the fine Ni particles and enhanced H2 and CO2 chemisorption and activation properties resulted in boosting the catalytic activity of both CO2 methanation and CH4-CO2 reforming reactions. The Ni/Mg ratios and the reduction temperatures were detailed optimized, and the 600oC-reduced Ni8Mg2-NT catalyst with the Ni/Mg ratio of 8:2 was the optimal, which also exhibited high long-term stability. In short, the formed Ni-Mg-phyllosilicate solid solution structure and the special interactions of different species brought about high catalytic performance of the nanotubular Ni-Mg phyllosilicate catalyst.

The role of surface hydroxyls on ZnZrOx solid solution catalyst in CO2 hydrogenation to methanol

ZnZrOx solid solution catalyst is an excellent catalyst in methanol synthesis from CO2 hydrogenation. It is still highly aspiration to make any further improvement in catalytic performance. In this work, ZnZrOx solid solution catalyst is prepared with different methods, resulting in different surface property. The ZnZrOx solid solution catalyst prepared by reflux ammonia (ZnZrOx-RA) exhibits higher methanol selectivity of 95.2% and CO2 conversion of 3.3% than that of the catalyst obtained via co-precipitation (ZnZrOx-CP) at 280 °C, 5 MPa. Subsequent kinetics analysis shows that ZnZrOx-RA, in comparison to ZnZrOx-CP, shows a decreased activation energy for methanol synthesis, an increased reaction order in H2, and a similar reaction order in CO2. Structural characterizations indicate that these two catalysts are in solid solution state, while ZnZrOx-RA possesses more Zn-OH species on the surface. The surface Zn-OH species enhance the activation and adsorption of CO2 and H2, and improve the generation and stability of HCOO* species, which promote CO2 hydrogenation to methanol.

Synthesis of C3+ alcohols through ethanol condensation and carbon-carbon coupling of ethanol with CO2

C3+ alcohols are widely used as organic solvents, raw chemicals and fuel additives. However, the self-condensation of alcohol can limit the distribution of products. Herein, the binary metal oxide ZnO-ZrO2 with solid solution structure was prepared and applied into the synthesis of higher alcohols through the ethanol condensation and the coupling of ethanol with the CO2 hydrogenation. The optimized 0.3ZnO-ZrO2 solid-solution catalyst shows that ethanol conversion can reach 29% with the C3+ alcohols (1-propanol, 1-butanol and 1-hexanol) selectivity of 67%. The high selectivity of C3+ alcohols can be attributed to the acid-base bifunction for performing the condensation of ethanol and the coupling of ethanol and the CHxO intermediates that are produced through CO2 hydrogenation. This work opens a new avenue for the synthesis of C3+ alcohols.

Intrinsically robust cubic MnCoOx solid solution: achieving high activity for sustainable acidic water oxidation

The MnCoOx solid solution catalysts show excellent catalytic efficiency and stability in the acidic OER. The investigation and DFT studies highlight the essential role of Co3+ and Mn4+ cations and oxygen vacancies in the OER mechanism.