Highly Active Hydrogen-rich Photothermal Reverse Water Gas Shift Reaction on Ni/LaInO3 Perovskite Catalysts with Near-unity Selectivity

Photo-assisted reverse water gas shift (RWGS) reaction is regarded green and promising in controlling the reaction gas ratio in Fischer Tropsch synthesis. But it is inclined to produce more byproducts in high H₂ concentration condition. Herein, LaInO₃ loaded with Ni-nanoparticles (Ni NPs) was designed to obtain an efficient photothermal RWGS reaction rate, where LaInO₃ was enriched with oxygen vacancies to roundly adsorbing CO₂ and the strong interaction with Ni NPs endowed the catalysts with powerful H₂ activity. The optimized catalyst performed a large CO yield rate (1314 mmol g_Ni⁻¹ h⁻¹) and ≈100 % selectivity. In situ characterizations demonstrated a COOH* pathway of the reaction and photoinduced charge transfer process for reducing the RWGS reaction active energy. Our work provides valuable insights on the construction of catalysts concerning products selectivity and photoelectronic activating mechanism on CO₂ hydrogenation.     

FeMn、FeMnNa和FeMnK催化剂上合成气制低碳烯烃的比较

研究了钠、钾助剂对FeMn 合成低碳烯烃催化剂结构及性能的影响. 低温N₂吸附、X射线光电子能谱（XPS）、X射线衍射（XRD）、H₂程序升温还原（H₂-TPR）、CO/CO₂程序升温脱附（CO/CO₂-TPD）、Mössbauer 谱和CO+H₂反应的研究结果表明,增加Mn助剂含量促进了活性相的分散和低碳烯烃的生成,而过多锰助剂在催化剂表面的富集则降低了费托合成反应的CO转化率;钾助剂和钠助剂的加入均抑制了催化剂的还原并且促进了CO₂和CO的吸附. 比较还原后（H₂/CO摩尔比为20）和反应后（H₂/CO摩尔比为3.5）催化剂的体相结构可以发现,在FeMn、FeMnNa和FeMnK催化剂中,由于钾助剂的碱性和CO吸附能力较强,因此体相中FeC_x的含量相对较高;而活性测试结果表明,FeMnNa催化剂拥有最好的CO转化率（96.2%）和低碳烯烃选择性（30.5%,摩尔分数）.     

Efficient Ni-based catalysts for low-temperature reverse water-gas shift (RWGS) reaction

CO₂ hydrogenation for syngas can alleviate the pressure of un-controlled emissions of CO₂ and bring enormous economic benefits. Advantageous Ni-catalysts have good CO₂ hydrogenation activity and high CO selectivity merely over 700 °C. Herein, we introduced Cu into Ni catalysts, which were evaluated by H₂-TPR, XRD, BET, in-situ XPS and CO₂-TPD, and their CO₂ hydrogenation activity and CO selectivity were significantly affected by the Ni/Cu ratios, which was rationalized by the synergistic effect of bimetallic catalysts. In addition, the reduction temperatures of studied catalysts apparently affected the CO₂ hydrogenation, which were caused by the number and dispersion of the active species. It's found that the Ni₁Cu₁-400 had good stability, high CO selectivity (up to 90%), and fast formation rate (1.81×10⁻⁵ mol/g_cat/s) at 400 °C, which demonstrated a good potential as a superior catalyst for reverse water-gas shift (RWGS) reaction.     

Theoretical Investigation of Reverse Water Gas Shift Reaction Catalyzed by Ruthenium Halogen Carbonyl Complexes

In this paper we present theoretical study of the reverse water gas shift (RWGS) reaction catalyzed by ruthenium halogen carbonyl complexes. Three mechanisms, including hydrogen chloride, formic acid and oxidation–reduction mechanism, have been explored by density functional theory. The calculations indicate that the oxidation–reduction mechanism contributes to the TDI and TDTS in the ESM TOF calculations. Bimetallic catalysts would be likely to be more highly active than monometallic catalyst for the RWGS reaction. Among bimetallic catalysts studied, both bimetallic catalysts [Ru(μ-Cl)Cl(CO)₃]₂ and [Ru(μ-CO)Cl(CO)₃]₂ shows higher activity than [Ru(μ-Cl)(CO)₄]₂ catalyst with [Ru(μ-CO)Cl(CO)₃]₂ considering as the most efficient catalyst for RWGS reaction.     

Tuning product selectivity in CO2 hydrogenation over metal-based catalysts

Conversion of CO₂ into chemicals is a promising strategy for CO₂ utilization, but its intricate transformation pathways and insufficient product selectivity still pose challenges. Exploiting new catalysts for tuning product selectivity in CO₂ hydrogenation is important to improve the viability of this technology, where reverse water-gas shift (RWGS) and methanation as competitive reactions play key roles in controlling product selectivity in CO₂ hydrogenation. So far, a series of metal-based catalysts with adjustable strong metal–support interactions, metal surface structure, and local environment of active sites have been developed, significantly tuning the product selectivity in CO₂ hydrogenation. Herein, we describe the recent advances in the fundamental understanding of the two reactions in CO₂ hydrogenation, in terms of emerging new catalysts which regulate the catalytic structure and switch reaction pathways, where the strong metal–support interactions, metal surface structure, and local environment of the active sites are particularly discussed. They are expected to enable efficient catalyst design for minimizing the deep hydrogenation and controlling the reaction towards the RWGS reaction. Finally, the potential utilization of these strategies for improving the performance of industrial catalysts is examined.

A series of metal oxide, phosphate, alloy, and carbide-based catalysts for selective CO₂ hydrogenation are summarized, showing their abilities to switch CO₂ methanation to RWGS.     

Preparation and operating conditions for cobalt cerium oxide catalysts used in the conversion of synthesis gas into light olefins

Cobalt cerium oxides, prepared using a co-precipitation procedure, were studied as catalysts for the conversion of synthesis gas to light olefins (C₂-C₄). Specifically, we studied the effect of a range of preparation variables, including the molar ratio of the [Co]/[Ce] of the precipitation solution, ageing time and calcination temperature. In addition, the effects of supports and promoters on the catalysts’ activity and selectivity and a range of reaction temperatures using synthesis gas with different H₂/CO molar feed ratios were investigated. The catalyst containing a molar ratio of 80% Co and 20% Ce, aged for 2 h, supported with 15 wt% SiO₂ without any promoter, at an operating temperature of 450 °C and an H₂/CO feed ratio of 2/1 (GHSV = 4500 h^?1), performed optimally for the conversion of synthesis gas to light olefins. The characterization of both the precursors and the calcined catalysts by powder X-ray diffraction, scanning electron microscopy, Brunauer-Emmett-Teller specific surface area measurements and thermal analysis methods, including TGA and DSC, show that all the preparation variables influenced the catalyst precursor structure.     

Mechanism of the Reverse Water–Gas Shift Reaction Catalyzed by Cu<Subscript>12</Subscript>TM Bimetallic Nanocluster: A Density Functional Theory Study

Density functional theory calculations were carried out to investigate Cu₁₂TM (TM = Co, Rh, Ir, Ni, Pd, Pt, Ag, Au) bimetallic metal catalysts for the mechanism of reverse water–gas shift (RWGS) reaction. The three possible reaction pathways relevant to the RWGS reaction are explored, including the CO₂ dissociation, carboxyl, and formate mechanisms. Our results indicate that the RWGS reaction prefers to follow the CO₂ dissociation mechanism on Cu₁₂TM surfaces. A detailed potential energy diagram of the kinetically favored mechanism is presented that shows that the RDS of reaction are the formation of H₂O and carboxyl (HOCO), formate (HCOO) dissociation, respectively. And, Cu₁₂TM (TM = Co, Pt) are lower than other catalysts from the energy barrier of elementary step. Moreover, the catalytic behavior of a Cu₁₂TM cluster is changed significantly due to the modifiers, via the electron transfer from TM to Cu-based cluster, and the activation barrier decreases with doped TM. The turnover frequency of the Cu₁₂Co is the highest value, which thus is more efficiency catalyst to RWGS reaction. To gain insights into the synergistic effect in catalytic activity of the Cu₁₂TM bimetallic cluster, a projected density of states analysis has been performed. Our works will be important for predicting the energetic trends and designing a better catalyst of RWGS reaction.     

预处理对Ni-Co双金属沼气重整催化剂性能与结构的影响

采用过量浸渍法制备了Ni-Co/La₂O₃-γ-Al₂O₃双金属催化剂, 并使用固定床石英反应器在850℃,0.1MPa和空速为6000mL g_cat^-1 h^-1的条件下考察了预处理对催化剂性能的影响. 运用X射线衍射、热重-差示扫描量热、透射电子显微镜、扫描电镜和X射线能谱分析等手段对催化剂进行了表征. 结果表明,与传统氢气还原预处理相比,经氢气和二氧化碳预处理后, 催化剂性能明显提高,且能基本消除该催化剂上沼气重整反应的诱导期. 511 h的稳定性实验结果表明,催化剂经氢气和二氧化碳预处理后具有很好的稳定性和抗积碳性,平均积碳速率仅为0.2 mg g_cat^-1 h^-1. 表征结果显示,经氢气和二氧化碳预处理后,催化剂具有更好的抗烧结和抗积碳性能,反应后金属颗粒较小,分布较均匀,粒径分布范围较窄,从而增强了催化剂的稳定性.     

Platinum and Frustrated Lewis Pairs on Ceria as Dual-Active Sites for Efficient Reverse Water-Gas Shift Reaction at Low Temperatures

The low-temperature reverse water-gas shift (RWGS) reaction faces the following obstacles: low activity and unsatisfactory selectivity. Herein, the dual-active sites of platinum (Pt) clusters and frustrated Lewis pair (FLP) on porous CeO₂ nanorods (Pt_cluster/PN−CeO₂) provide an interface-independent pathway to boost high performance RWGS reaction at low temperatures. Mechanistic investigations illustrate that Pt clusters can effectively activate and dissociate H₂. The FLP sites, instead of the metal and support interfaces, not only enhance the strong adsorption and activation of CO₂, but also significantly weaken CO adsorption on FLP to facilitate CO release and suppress the CH₄ formation. With the help of hydrogen spillover from Pt to PN−CeO₂, the Pt_cluster/PN−CeO₂ catalysts achieved a CO yield of 29.6 %, which is very close to the thermodynamic equilibrium yield of CO (29.8 %) at 350 °C. Meanwhile, the Pt_cluster/PN−CeO₂ catalysts delivered a large turnover frequency of 8720 h⁻¹. Moreover, Pt_cluster/PN−CeO₂ operated stably and continuously for at least 840 h. This finding provides a promising path toward optimizing the RWGS reaction.     

Widely Controllable Syngas Production by a Dye‐Sensitized TiO2 Hybrid System with ReI and CoIII Catalysts under Visible‐Light Irradiation

Visible‐light irradiation of a ternary hybrid catalyst prepared by grafting a dye, an H₂ evolving Co^III catalyst and a CO‐producing Re^I catalyst on TiO₂ have been found to produce both H₂ and CO (syngas) in CO₂‐saturated N ,N ‐dimethyl formamide (DMF)/water solution containing a 0.1 m sacrificial electron donor. The H₂/CO ratios are effectively controlled by changing either the water content of the solvent or the molar ratio of the Re^I and Co^III catalysts ranging from 1:2 to 15:1. The controlled syngas formation is discussed in terms of competitive electron flow from TiO₂ to each of the CO₂‐reduction and hydrogen‐evolving sites depending on the efficiencies of the two catalytic reaction cycles under given reaction conditions.     

Hydrogenation of Carbon Dioxide on Iron Manganese Catalysts

The synthesis of hydrocarbons from hydrogenation of carbon dioxide has been studied on a series of coprecipitated iron-manganese catalysts. Kinetic measurements, X-ray diffraction, Mössbauer spectroscopy, and temperature-programmed reaction of adsorbed species were used for activity tests and catalyst characterizations. The results showed that the yields of low-carbon olefins decrease, whereas the amount of methane increases with increasing manganese content in catalysts. The conversion to hydrocarbons is suppressed by the reverse water-gas shift (RWGS) reaction equilibrium. Mössbauer spectra and XRD patterns of catalysts after reaction indicate that catalysts are severely oxidized; it is speculated that the olefin producing surface structure in CO hydrogenation may be destroyed by this oxidation. A pulse-reactor study of the Boudouard reaction showed that manganese has the effect of suppressing CO dissociation and thus decreasing carbon content on catalysts. For CO₂ hydrogenation, the affinity to carbon on catalysts is important; therefore manganese is not a good promoter. Among all catalysts tested, pure iron has the best selectivity to olefinic and long-chain hydrocarbons.     

Effect of methane co-feeding on the selectivity of ethylene produced from oxidative dehydrogenation of ethane with CO2 over a Ni-La/SiO2 catalyst

A Ni-La/SiO₂ catalyst was prepared through the incipient wetness impregnation method and tested in the oxidative dehydrogenation of ethane (ODHE) with CO₂. The fresh and used catalysts were characterized by XRD and SEM techniques. The Ni-La/SiO₂ catalyst exhibited catalytic activity for the oxidative dehydrogenation of ethane, but with low ethylene selectivity in the absence of methane. The selectivity to ethylene increased with increasing molar ratio of methane in the feed. The carbon deposited on the catalyst surface in the sole ODHE with CO₂ was mainly inert carbon, while much more filamentous carbon was formed in the presence of methane. The filamentous carbon was easy to be removed by CO₂, which might play a role in improving the conversion of ethane to ethylene. The introduction of methane might affect the equilibrium of the CO₂ reforming of ethane and the ODHE with CO₂. As a consequence, the synthesis gas produced from CO₂ reforming of methane partly inhibited the reaction of ethane and promoted the ODHE with CO₂, thus increasing the selectivity of ethylene.     

Hydroisomerization of n-heptane over bimetal-bearing H3PW12O40 catalysts supported on dealuminated USY zeolite

The bimetal-bearing (CePt or LaPt) 12-tungstophosphoric acid (H₃PW₁₂O₄₀ (PW)) catalysts supported on dealuminated USY zeolite (DUSY) were prepared by impregnation and characterized by XRD, BET, IR, and H₂-chemisorption. Their catalytic activities were tested in the hydroisomerization of n-heptane with a continuous atmospheric fixed-bed reactor. After the steam treatment combined with the acid leaching, as well as the supporting with PW and the bimetals, the DUSY support retains the Y zeolite porosity and the PW well keeps its Keggin structure in catalysts. The doping of Ce into the catalysts enhances the dispersion of Pt on the catalyst surface. The Pt-bearing PW catalysts doped with Ce or La, especially Ce, exhibit much higher catalytic activity and selectivity than the catalysts without dopants at lowered reaction temperatures. At the optimal reaction conditions, i.e., the reaction temperature of 250°C and WHSV of 1.4 h^?1, the catalyst with a Pt loading of 0.4%, PW loading of 10% and a molar ratio of Ce to Pt of 15:1 shows a conversion of n-heptane of 70.3% with a high selectivity for isomerization products of 94.1%.     

Role of preparation parameters of Cu–Zn mixed oxide catalyst in solvent free glycerol carbonylation with urea

Solvent-free carbonylation of glycerol with urea to glycerol carbonate (GC) was achieved over heterogeneous Cu–Zn mixed oxide catalyst. Cu–Zn catalysts with different ratios of Cu:Zn were prepared using co-precipitation (CP) and oxalate gel (OG) methods. As compared to CuO–ZnO(2:1) catalyst prepared by oxalate gel (OG) method, much higher conversion of glycerol and highest selectivity towards glycerol carbonate (GC) was achieved with CuO–ZnO_CP(2:1) catalyst. Physicochemical properties of prepared catalysts were investigated by using XRD, FT-IR, BET, TPD of CO₂ and NH₃ and TEM techniques. The effect of stoichiometric ratio of Cu/Zn, calcination temperature of CuO–ZnO catalysts and effect of reaction parameters such as molar ratio of substrates, time and temperature on glycerol conversion to GC were critically studied. Cu/Zn of 2:1 ratio, glycerol–urea 1:1 molar ratio, 145 ​°C reaction temperatures were found to be optimized reaction conditions to achieve highest glycerol conversion of 86% and complete selectivity towards GC. The continuous expel of NH₃ from reaction the mixture avoided formation of ammonia complex with CuO–ZnO catalyst. As a result of this, CuO–ZnO catalyst could be recycled up to three times without losing its initial activity.     

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.     

钾调变Mo/SBA-15催化剂用于乙烷选择氧化制乙醛

采用两步浸渍法制备钾改性的Mo/SBA-15 催化剂. 采用N₂吸附,X射线衍射（XRD）,透射电镜（TEM）,紫外-可见（UV-Vis）吸收光谱,拉曼（Raman）光谱,NH₃程序升温脱附（NH₃-TPD）,CO₂程序升温脱附（CO₂-TPD）,H₂程序升温还原（H₂-TPR）等手段表征催化剂的物理化学性质. 研究结果表明,在Mo_0.75/SBA-15 中添加K之后,有新物种钾钼酸盐生成,并且当K/Mo的摩尔比不同时,钼物种的存在状态也不同. 添加钾之后,催化剂的活性和总醛（甲醛、乙醛、丙烯醛）的选择性均有所提高,并且受钾的添加量影响. 在575 ℃时,在K_0.25-Mo_0.75/SBA-15催化剂上醛的收率可高达8.5%（摩尔分数）.     

Turning it off! Disfavouring hydrogen evolution to enhance selectivity for CO production during homogeneous CO2 reduction by cobalt–terpyridine complexes

Understanding the activity and selectivity of molecular catalysts for CO₂ reduction to fuels is an important scientific endeavour in addressing the growing global energy demand. Cobalt–terpyridine compounds have been shown to be catalysts for CO₂ reduction to CO while simultaneously producing H₂ from the requisite proton source. To investigate the parameters governing the competition for H⁺ reduction versus CO₂ reduction, the cobalt bisterpyridine class of compounds is first evaluated as H⁺ reduction catalysts. We report that electronic tuning of the ancillary ligand sphere can result in a wide range of second-order rate constants for H⁺ reduction. When this class of compounds is next submitted to CO₂ reduction conditions, a trend is found in which the less active catalysts for H⁺ reduction are the more selective towards CO₂ reduction to CO. This represents the first report of the selectivity of a molecular system for CO₂ reduction being controlled through turning off one of the competing reactions. The activities of the series of catalysts are evaluated through foot-of-the-wave analysis and a catalytic Tafel plot is provided.     

A new kinetic model for direct CO_2 hydrogenation to higher hydrocarbons on a precipitated iron catalyst:Effect of catalyst particle size

The kinetic of the direct CO_2 hydrogenation to higher hydrocarbons via Fischer–Tropsch synthesis(FTS)and reverse water-gas shift reaction(RWGS) mechanisms over a series of precipitated Fe/Cu/K catalysts with various particle sizes was studied in a well mixed, continuous spinning basket reactor. The iron catalysts promoted with copper and potassium were prepared via precipitation technique in various alcohol/water mixtures to achieve a series of catalyst particle sizes between 38 and 14 nm. A new kinetic model for direct CO_2 hydrogenation was developed with combination of kinetic model for FTS reaction and RWGS equilibrium condition. For estimate of structure sensitivity of indirect CO_2 hydrogenation to higher hydrocarbons, the kinetic parameters of developed model are evaluated for a series of iron catalysts with various particle sizes. For kinetic study a wide range of syngas conversions have been obtained by varying experimental conditions. The results show that the new developed model fits favorably with experimental data. The values of activation energies for indirect CO_2 hydrogenation reaction are fall within the narrow range of 23–16 kJ/mol.     

Photo-Induced Switching of CO2 Hydrogenation Pathway towards CH3OH Production over Pt@UiO-66-NH2(Co)

It is highly desired to achieve controllable product selectivity in CO₂ hydrogenation. Herein, we report light-induced switching of reaction pathways of CO₂ hydrogenation towards CH₃OH production over actomically dispersed Co decorated Pt@UiO-66-NH₂. CO, being the main product in the reverse water gas shift (RWGS) pathway under thermocatalysis condition, is switched to CH₃OH via the formate pathway with the assistance of light irradiation. Impressively, the space-time yield of CH₃OH in photo-assisted thermocatalysis (1916.3 μmol g_cat⁻¹ h⁻¹) is about 7.8 times higher than that without light at 240 °C and 1.5 MPa. Mechanism investigation indicates that upon light irradiation, excited UiO-66-NH₂ can transfer electrons to Pt nanoparticles and Co sites, which can efficiently catalyze the critical elementary steps (i.e., CO₂-to-*HCOO conversion), thus suppressing the RWGS pathway to achieve a high CH₃OH selectivity.     

TiO2 supported cobalt-manganese nano catalysts for light olefins production from syngas

Cobalt-manganese nano catalysts were prepared by sol-gel method. This research investigated the effects of different cobalt-manganese (Co/Mn = 1/1) loading, pH and calcination conditions on the catalytic performance of Co-Mn/TiO₂ catalysts for Fischer-Tropsch synthesis (FTS) in a fixed bed reactor. It was found that the catalyst containing 30wt%(Co-Mn)/TiO₂ was an optimal catalyst for the conversion of synthesis gas to light olefins especially propylene. The activity and selectivity of optimal catalyst were studied under different operational conditions. The results showed that the best operational conditions were H₂/CO= 1/1 molar feed ratio at 250 °C and GHSV= 1300 h^?1 under atmospheric pressure. Characterization of catalysts was carried out by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N₂ adsorption-desorption measurements.