Physicochemical characteristic of neodymium oxide-based catalyst for in-situ CO2/H2 methanation reaction

Carbon dioxide emission to the atmosphere is worsened as all the industries emit greenhouse gases (GHGs) to the atmosphere, particularly from refinery industries. The catalytic chemical conversion through methanation reaction is the most promising technology to convert this harmful CO₂ gas to wealth CH₄ gas for the combustion. Thus, supported neodymium oxide based catalyst doped with manganese and ruthenium was prepared via wet impregnation route. The screening was initiated with a series of Nd/Al₂O₃ catalysts calcined at 400?°C followed by optimization with respect to calcination temperatures, based ratios loading and various Ru loading. The Ru/Mn/Nd (5:20:75)/Al₂O₃ calcined at 1000?°C was the potential catalyst, attaining a complete CO₂ conversion and forming 40% of CH₄ at 400?°C reaction temperature. XRD results revealed an amorphous phase with the occurrence of active species of RuO₂, MnO_2, and Nd₂O₃, and the mass ratio of Mn was the highest among other active species as confirmed by EDX. The ESR resulted in the paramagnetic of Nd³⁺ at the g value of 2.348. Meanwhile nitrogen adsorption (NA) analysis showed the Type IV isotherm which exhibited the mesoporous structure with H3 hysteresis of slit shape pores.     

Promotion effect of additive Fe on Al2O3 supported Ni catalyst for CO2 methanation

In this paper, the effect of additive Fe on Ni/Al₂O₃ catalyst for CO₂ methanation was studied. A series of bimetallic Ni–Fe catalysts with different Ni/Fe ratios were prepared by impregnation method. For comparison, monometallic Fe‐based and Ni‐based catalysts were also prepared by the same method. The characterization results showed that adding Fe to Ni catalyst on the premise of a low Ni loading(≦12 wt.%) enhanced CO₂ methanation performance. However, when the Ni loading reached 12 wt.%, the catalytic activity decreased with the increase of Fe content, but still higher than the corresponding Ni‐based catalyst without Fe. Among them, the 12Ni3Fe catalyst exhibited the highest CO₂ conversion of 84.3 % and nearly 100% CH₄ selectivity at 50000 ml g^‐1 h^‐1 and 420 °C. The enhancement effect of adding Fe on CO₂ methanation was attributed to the dual effect of suitable electronic environment and increased reducibility generated by Fe species.     

A Biomass-Ligand-Based Ru(III) Complex as a Catalyst for Cycloaddition of CO2 and Epoxides to Cyclic Carbonates and a Study of the Mechanism

Aiming highly efficient conversion of greenhouse gas CO₂ to cyclic carbonates, a biomass Ru(III) Schiff base complex catalyst ( SalRu ) was constructed by employing a derivative of Lignin degradation (5-aldehyde vanillin). The SalRu catalyst had a remarkable conversion for epoxides into corresponding cyclic carbonates even at atmospheric pressure of CO₂ without the presence of co-catalyst. As the condition at 120 °C and 2 MPa CO₂ the conversion reached to 94 % with selectivity at 99 % after 8 h. 32 % cyclic carbonate production was obtained even under 0.2 MPa CO₂ pressure. The epoxide activation and ring opening, CO₂ insertion and cyclic carbonate formation were illuminated explicitly through the of characteristic absorption peaks changing, which further providing direct and visual evidence for the mechanism proposing. This study has important theoretical significance for the comprehensive utilization of environmental pollutants and energy.     

Bipyridine‐Assisted Assembly of Au Nanoparticles on Cu Nanowires To Enhance the Electrochemical Reduction of CO2

We report a new strategy to prepare a composite catalyst for highly efficient electrochemical CO₂ reduction reaction (CO₂RR). The composite catalyst is made by anchoring Au nanoparticles on Cu nanowires via 4,4′‐bipyridine (bipy). The Au‐bipy‐Cu composite catalyzes the CO₂RR in 0.1 m KHCO₃ with a total Faradaic efficiency (FE) reaching 90.6 % at ?0.9 V to provide C‐products, among which CH₃CHO (25 % FE) dominates the liquid product (HCOO^?, CH₃CHO, and CH₃COO^?) distribution (75 %). The enhanced CO₂RR catalysis demonstrated by Au‐bipy‐Cu originates from its synergistic Au (CO₂ to CO) and Cu (CO to C‐products) catalysis which is further promoted by bipy. The Au‐bipy‐Cu composite represents a new catalyst system for effective CO₂RR conversion to C‐products.     

Tin(II)-Based Metal–Organic Frameworks Enabling Efficient,Selective Reduction of CO2 to Formate under Visible Light

Certain metal complexes are known as high-performance CO₂ reduction photocatalysts driven by visible light. However, most of them rely on rare, precious metals as principal components, and integrating the functions of light absorption and catalysis into a single molecular unit based on abundant metals remains a challenge. Metal-organic frameworks (MOFs), which can be regarded as intermediate compounds between molecules and inorganic solids, are potential platforms for the construction of a simple photocatalytic system composed only of Earth-abundant nontoxic elements. In this work, we report that a tin-based MOF enables the conversion of CO₂ into formic acid with a record high apparent quantum yield (9.8 % at 400 nm) and >99 % selectivity without the need for any additional photosensitizer or catalyst. This work highlights a new MOF with strong potential for photocatalytic CO₂ reduction driven by solar energy.     

Multidisciplinary green approaches (ultrasonic,co-precipitation,hydrothermal, and microwave) for fabrication and characterization of Erbium-promoted Ni-Al2O3 catalyst for CO2 methanation

The dispersion of nickel catalysts is crucial for the catalytic ability of CO₂ methanation, which can be influenced by the fabrication method and the operation process of the catalysts. Therefore, a series of fabrication methods, including ultrasonic, hydrothermal, microwave, and co-precipitation, have been applied to prepare 25Ni-5Er-Al₂O₃ catalysts. The fabrication method can partially influence the structural and catalytic activity of the nickel aluminate catalysts. Among the catalysts modified by Erbium prepared with various methods, the catalyst fabricated by ultrasonic pathway exhibited better catalytic performance and CH₄ selectivity especially, at a temperature (400 ℃). The impact of the temperature of the reaction (200–500 °C) was examined under a stoichiometric precursor ratio of (H₂:CO₂) = 4: 1, atmospheric pressure, and space velocity (GHSV) of 25000 mL/gcath. The results demonstrate that the ultrasonic method is strongly efficient for fabricating Ni-based catalysts with a high BET surface area of about 190.33 m²g^?1. The catalyst composed via the ultrasonic technique has 69.38 % carbon dioxide conversion and 100 % methane selectivity at 400 °C for excellent catalytic performance in CO₂ methanation reactions. The fabrication effect can be associated with its high surface area, which is achieved via the hot spot mechanism. Besides, the addition of Erbium promotes the Ni dispersion on the supports and stimulates the positive reaction because of the erbium oxygen vacancies.     

Formation and Conversion of Surface Compounds upon Interaction of Ethanol with Cu/CeO<Subscript>2</Subscript> Catalyst According to in situ IR Spectroscopy

In the conditions of ethanol conversion on the surface of a 5%Cu/CeO₂ catalyst, the method of in situ IR spectroscopy reveals ethoxy groups, acetate and formiate complexes, and consolidation products. Acetaldehyde, acetone, croton aldehyde, butadiene, hydrogen, CO, and CO₂ are observed in the reaction products. As the temperature of the experiment increases, the concentration of acetaldehyde passes through a maximum at T = 250°C. This product is formed due to the interaction of ethoxy and hydroxyl surface groups. The concentration of acetone, croton aldehyde, and butadiene also passes through a maximum in the 350–400°C range. These products are associated with the decomposition of the consolidation products. The concentration of hydrogen, CO and CO₂ steadily increases with temperature and only these reaction products are left at T > 400°C. A mechanism of hydrogen formation based on the conversion of the highest temperature formiate surface complex is discussed.     

Regeneration of C4H10 dry reforming catalyst by nonthermal plasma

Carbon deposition via coke formation is one of the critical problems causing catalyst deactivation during the reforming of hydrocarbons. An effort was made to regenerate the catalyst (Ni/γ-alumina) by oxidation methods. Two approaches were carried out for the regeneration of the deactivated catalyst. The first one involves the plasma treatment of the deactivated catalyst in the presence of dry air over a temperature range of 300～500 °C, while the second one only the thermal treatment in the same temperature range. The performance of the regenerated catalyst was evaluated in terms of C₄H₁₀ and CO₂ conversions and the physicochemical characteristics were examined using a surface area analyzer, an elemental analyzer, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was observed that the carbon deposit (coke) on the catalyst was about 9.89 wt% after reforming C₄H₁₀ for 5 h at 540 °C. The simple thermal treatment at 400 °C reduced carbon content to 6.59 wt% whereas it was decreased to 3.25 wt% by the plasma and heat combination. The specific surface area was fully restored to the original state by the plasma-assisted regeneration at 500 °C. As far as the catalytic activity is concerned, the fresh and regenerated catalysts exhibited similar C₄H₁₀ and CO₂ conversion efficiencies.     

Optimization study by Box-Behnken design (BBD) and mechanistic insight of CO2 methanation over Ru-Fe-Ce/γ-Al2O3 catalyst by in-situ FTIR technique

The utilization of carbon dioxide for methanization reactions in the production of synthetic natural gas (SNG) is of increasing interest in energy-related issues. The use of CO₂ as a raw material in methanization reactions in the formation of SNG is of increasing concern associated with energy problems. The effect of three independent process parameters (calcination temperature, ceria loading and catalyst dosage) and their interactions in terms of conversion of CO₂ was considered by response surface methodology (RSM). Box-Behnken design (BBD) revealed that the optimized parameters were 1000 °C calcination temperature, 85%wt ceria loading and 10 g catalyst dosage, which resulted in 100% conversion of CO₂ and 93.5% of CH₄ formation. Reaction intermediate study by in situ FTIR showed that carboxylate species was the most active species on the catalyst surface. In-situ FTIR experiments revealed a weak CO₂ adsorption, that exist namely as carboxylate species over the trimetallic catalyst. As a result, dissociated hydrogen over ruthenium reacts with surface carbon, leading to *CH, which subsequently hydrogenated to produce *CH₂, *CH₃ and finally to the desired product methane. The use of in situ-FTIR study indicated that the CO₂ methanation mechanism does not involve CO as a reaction intermediate. The more detailed mechanism of CO₂ methanation pathways involved over Ru-Fe-Ce/γ-Al₂O₃ catalyst is discussed in accordance with IR-spectroscopic data. The better catalytic activity and stability over Ru-Fe-Ce (5:10:85)/γ-Al₂O₃ catalyst calcined at 1000 °C showed the presence of moderate basic sites for CO₂ adsorption.     

Unique catalysis of Ni-Al hydrotalcite derived catalyst in CO2 methanation: cooperative effect between Ni nanoparticles and a basic support

Ni-Al hydrotalcite derived catalyst (Ni-Al₂O₃-HT) exhibited a narrow Ni particle-size distribution with an average particle size of 4.0 nm. Methanation of CO₂ over this catalyst initiated at 225 °C and reached 82.5% CO₂ conversion with 99.5% CH₄ selectivity at 350 °C, which was much better than its impregnated counterpart. Characterizations by means of CO₂ microcalorimetry and ²⁷Al NMR indicated that large amount of strong basic sites existed on Ni-Al₂O₃-HT, originated from the formation of Ni-O-Al structure. The existence of strong basic sites facilitated the activation of CO₂ and consequently promoted the activity. The combination of highly dispersed Ni with strong basic support led to its unique and high efficiency for this reaction.     

Preparation,characterization and application of NiGaCu/MSO catalyst in conversion of carbon dioxide to methanol under mild pressure

In this paper, a novel catalyst was prepared based on NiGaCu alloys supported on ordered mesoporous silicon oxide (NiGaCu/MSO catalyst), through impregnation method. The impregnation was followed by drying the precipitation overnight, calcining it at 600 ​°C for 6 ​h under the air, and activating it in NaBH₄/ethanol solution at ambient temperature for 6 ​h. The NiGaCu/MSO catalyst was applied in conversion of CO₂ to CH₃OH by H₂ under mild pressure. The investigations over the prepared catalyst showed that the conversion could be carried out under pressure of 15 ​bar with very high conversion of CO₂ and good selectivity of CH₃OH compared to previous catalysts. The NiGaCu/MSO was characterized by many techniques including SAXRD, WAXRD, FT-IR, H₂-TPR, SEM and TEM. GC coupled with TCD and FID was used for determining the gas composition of the process.     

A study on methanol steam reforming to CO2 and H2 over the La2CuO4 nanofiber catalyst

The La₂CuO₄ crystal nanofibers were prepared by using single-walled carbon nanotubes as templates under mild hydrothermal conditions. The steam reforming of methanol (SRM) to CO₂ and H₂ over such nanofiber catalysts was studied. At the low temperature of 150 °C and steam/methanol=1.3, methanol was completely (100%, 13.8 g/h g catalyst) converted to hydrogen and CO₂ without the generation of CO. Within the 60 h catalyst lifespan test, methanol conversion was maintained at 98.6% (13.6 g/h g catalyst) and with 100% CO₂ selectivity. In the meantime, for distinguishing the advantage of nanoscale catalyst, the La₂CuO₄ bulk powder was prepared and tested for the SRM reaction for comparison. Compared with the La₂CuO₄ nanofiber, the bulk powder La₂CuO₄ showed worse catalytic activity for the SRM reaction. The 100% conversion of methanol was achieved at the temperature of 400 °C, with the products being H₂ and CO₂ together with CO. The catalytic activity in terms of methanol conversion dropped to 88.7% (12.2 g/h g catalyst) in 60 h. The reduction temperature for nanofiber La₂CuO₄ was much lower than that for the La₂CuO₄ bulk powder. The nanofibers were of higher specific surface area (105.0 m²/g), metal copper area and copper dispersion. The in situ FTIR and EPR experiments were employed to study the catalysts and catalytic process. In the nanofiber catalyst, there were oxygen vacancies. H₂-reduction resulted in the generation of trapped electrons [e] on the vacancy sites. Over the nanofiber catalyst, the intermediate H₂CO/HCO was stable and was reformed to CO₂ and H₂ by steam rather than being decomposed directly to CO and H₂. Over the bulk counterpart, apart from the direct decomposition of H₂CO/HCO to CO and H₂, the intermediate H₂COO might go through two decomposition ways: H₂COO=CO+H₂O and H₂COO=CO₂+H₂.     

Visible‐Light‐Driven CO2 Reduction by Mesoporous Carbon Nitride Modified with Polymeric Cobalt Phthalocyanine

The integration of molecular catalysts with low‐cost, solid light absorbers presents a promising strategy to construct catalysts for the generation of solar fuels. Here, we report a photocatalyst for CO₂ reduction that consists of a polymeric cobalt phthalocyanine catalyst (CoPPc) coupled with mesoporous carbon nitride (mpg‐CN_x) as the photosensitizer. This precious‐metal‐free hybrid catalyst selectively converts CO₂ to CO in organic solvents under UV/Vis light (AM 1.5G, 100 mW cm^?2, λ>300 nm) with a cobalt‐based turnover number of 90 for CO after 60 h. Notably, the photocatalyst retains 60 % CO evolution activity under visible light irradiation (λ>400 nm) and displays moderate water tolerance. The in situ polymerization of the phthalocyanine allows control of catalyst loading and is key for achieving photocatalytic CO₂ conversion.     

Co‐Catalyst‐Free Chemical Fixation of CO2 into Cyclic Carbonates by using Metal‐Organic Frameworks as Efficient Heterogeneous Catalysts

The concentration of carbon dioxide (CO₂) in the atmosphere is increasing at an alarming rate resulting in undesirable environmental issues. To mitigate this growing concentration of CO₂, selective carbon capture and storage/sequestration (CCS) are being investigated intensively. However, CCS technology is considered as an expensive and energy‐intensive process. In this context, selective carbon capture and utilization (CCU) as a C1 feedstock to synthesize value‐added chemicals and fuels is a promising step towards lowering the concentration of the atmospheric CO₂ and for the production of high‐value chemicals. Towards this direction, several strategies have been developed to convert CO₂, a Greenhouse gas (GHG) into useful chemicals by forming C?N, C?O, C?C, and C?H bonds. Among the various CO₂ functionalization processes known, the cycloaddition of CO₂ to epoxides has gained considerable interest owing to its 100% atom‐economic nature producing cyclic carbonates or polycarbonates in high yield and selectivity. Among the various classes of catalysts studied for cycloaddition of CO₂ to cyclic carbonates, porous metal‐organic frameworks (MOFs) have gained a special interest due to their modular nature facilitating the introduction of a high density of Lewis acidic (LA) and CO₂‐philic Lewis basic (LB) functionalities. However, most of the MOF‐based catalysts reported for cycloaddition of CO₂ to respective cyclic carbonates in high yields require additional co‐catalyst, say tetra‐n‐butylammonium bromide (TBAB). On the contrary, the co‐catalyst‐free conversion of CO₂ using rationally designed MOFs composed of both LA and LB sites is relatively less studied. In this review, we provide a comprehensive account of the research progress in the design of MOF based catalysts for environment‐friendly, co‐catalyst‐free fixation of CO₂ into cyclic carbonates.     

柠檬酸辅助固相研磨法制备铜基催化剂及在CO_2加氢合成甲醇反应中的性能研究

通过柠檬酸辅助固相研磨法制备铜基催化剂,采用XRD、TPR、TG-DSC、SEM、BET、TEM、XPS、CO_2-TPD等手段对催化剂性能进行表征.结果表明室温固相研磨的前驱体在惰性气体N_2中焙烧使体系中的CuO绝大部分被原位还原成Cu~0,不需外加H_2还原,直接制得了C/I-Cu/ZnO催化剂,催化剂具有中孔.利用高压固定床连续反应装置对催化剂活性进行了评价,结果表明,柠檬酸用量、前驱体焙烧温度、焙烧升温速率等条件对催化剂活性产生影响,当C_6H_8O_7/(Cu+Zn)摩尔比为1.2/1并Cu/Zn摩尔比1/1,前驱体在N_2中以3 K·min~(-1)升温速率于623 K焙烧3 h,制得的C/I-Cu/ZnO催化剂比表面积最大,Cu~0粒径最小,在CO_2加氢合成甲醇反应中表现出最佳的活性,CO_2转化率、甲醇选择性和产率分别达到了28.28%、74.29%和21.01%.与外加H_2还原的C/H-Cu/ZnO催化剂相比,原位还原C/I-Cu/ZnO催化剂比表面积较大,Cu~0的粒径较小,活性较高.     

The biogenic silica-derived Ni-phyllosilicate catalyst with Ru modification: effect of the hydroxylation enhancement and reduction procedure

Ni-phyllosilicate is difficultly formed on the surface of biogenic silica (E) extracted from equisetum fluviatile after calcination, resulting in poor catalytic activity at low temperature (<400 °C). In this work, the hydroxylation treatment of E was carried out to address the problem of lack of the surface silanol group and difficult formation of Ni-phyllosilicate, and the second metal Ru was added using a special procedure to further improve the activity of the catalyst. The surface silanol group concentration of silica (HE) was increased from 0.5 to 0.7 mmol/g after hydroxylation treatment, resulting in formation of more Ni-phyllosilicate with Ni content increase from 11.3 to 17.0 wt%. Considering the great gap of reduction difficulty of Ni-phyllosilicate (>800 °C) and RuO₂ species (190 °C), RuO₂ species was doped onto the 750 °C-pre-reduced Ni-phyllosilicate via impregnation, and metallic Ru together with Ni could be obtained simultaneously after reduction at a low temperature of 400 °C. The obtained Ru-modified Ni-phyllosilicate catalyst showed high CO₂ conversion of 77.3% and CH₄ selectivity of 96.4% with high turnover frequency (1.22 s^?1, 180 °C) and low activation energy (71.25 kJ/mol). In situ Diffused Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) results revealed that more active formate intermediates (m-HCOO- and m-CO₃^2?) result in high catalytic activity of the Ru-modified Ni-phyllosilicate catalyst. In addition, this catalyst exhibited high anti-sintering property, long-term stability, and hydrothermal stability under severe conditions owing to the Ni-phyllosilicate–based structure.     

生物质焦油组分甲苯在镍/凹凸棒石上的二氧化碳催化重整

 以大比表面积的天然纳米矿物材料凹凸棒石 (PG) 为载体, 采用等体积浸渍法制备了 Ni/PG 催化剂. 运用 X 射线衍射、透射电镜和 CO₂ 程序升温脱附对 Ni/PG 催化剂进行了表征, 并用于以甲苯为生物质焦油模型化合物的 CO₂ 催化重整反应. 考察了反应温度、CO₂ 浓度以及催化剂中 Ni 负载量对甲苯与 CO₂ 重整性能的影响. 结果表明, 吸附在催化剂表面的 CO₂ 存在三个脱附峰, 其中高温脱附 CO₂ 与反应密切相关; 随着 CO₂ 浓度、Ni 负载量和反应温度的增加, 甲苯转化率和 H₂ 产率升高. 在 800 ^oC, CO₂/PhCH₃ 摩尔比为 0.2~0.26 时, 甲苯转化率达最高; 而在 CO₂/PhCH₃ 摩尔比为 0.2 时, H₂ 产率最高. 催化剂上积炭量随 CO₂ 浓度的增加和反应温度的升高而显著降低.     

Solar-Driven CO2 Conversion via Optimized Photothermal Catalysis in a Lotus Pod Structure

Photothermal CO₂ reduction is one of the most promising routes to efficiently utilize solar energy for fuel production at high rates. However, this reaction is currently limited by underdeveloped catalysts with low photothermal conversion efficiency, insufficient exposure of active sites, low active material loading, and high material cost. Herein, we report a potassium-modified carbon-supported cobalt (K⁺−Co−C) catalyst mimicking the structure of a lotus pod that addresses these challenges. As a result of the designed lotus-pod structure which features an efficient photothermal C substrate with hierarchical pores, an intimate Co/C interface with covalent bonding, and exposed Co catalytic sites with optimized CO binding strength, the K⁺−Co−C catalyst shows a record-high photothermal CO₂ hydrogenation rate of 758 mmol g_cat⁻¹ h⁻¹ (2871 mmol g_Co⁻¹ h⁻¹) with a 99.8 % selectivity for CO, three orders of magnitude higher than typical photochemical CO₂ reduction reactions. We further demonstrate with this catalyst effective CO₂ conversion under natural sunlight one hour before sunset during the winter season, putting forward an important step towards practical solar fuel production.     

Ni/MgO catalyst prepared using atmospheric high-frequency discharge plasma for CO2 reforming of methane

A new type of Ni/MgO catalyst was prepared using atmospheric high-frequency discharge cold plasma. The influences of conventional method, plasma method, and plasma plus calcination method on the catalytic activity were studied and the CO2 reforming of methane was chosen as the probe reaction. The catalysts were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), X-ray photoelectron spectroscopy, and CO2 temperature-programmed surface reaction techniques. The results suggested that the nickel-based catalyst prepared by plasma plus calcination method possessed a smaller particle size and a higher dispersion of active component, better low-temperature activity and enhanced anti-coking ability. The conversion of CO2 and CH4 was 90.70% and 89.37%, respectively, and the reaction lasted for 36 h without obvious deactivation under 101.325 kPa and 750°C with CO2/CH4 = 1/1.     

Study of CuZnMOx oxides (M = Al,Zr, Ce,CeZr) for the catalytic hydrogenation of CO2 into methanol

CuO–ZnO–Al₂O₃ catalysts were synthesized by two methods, sol–gel and co-precipitation syntheses. Al₂O₃ was then substituted with other supports, such as ZrO₂, CeO₂ and CeO₂–ZrO₂ in order to have a better understanding of the support's effect. These catalysts containing 30 wt% of Cu were then tested for CO₂ hydrogenation into methanol. The effect of reaction temperature and GHSV on the catalytic behaviour was also investigated. The best results were obtained with a 30 CuO–ZnO–ZrO₂ catalyst synthesized by co-precipitation and calcined at 400 °C. This catalyst presents a good CO₂ conversion rate (23%) with 33% of methanol selectivity, leading to a methanol productivity of 331 g_MeOH.kg_cata⁻¹·h⁻¹ at 280 °C under 50 bar and a GHSV of 10,000 h⁻¹.