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.     

Asymmetric hydrogenation of quinolines with recyclable and air-stable iridium catalyst systems

The iridium complex-catalyzed asymmetric hydrogenation of quinolines in a DMPEG/hexane biphasic system was studied. Catalysts with C₂-symmetric ligands such as Xyl-P-Phos, Cl–MeO–BIPHEP, SYNPHOS, and DifluorPhos are highly effective for this type of reaction. Most of the catalysts tested can be retained in DMPEG (M_n = 500), and the asymmetric hydrogenation of various quinoline substrates can be carried out in DMPEG/hexane biphasic system with up to 92% ee. The catalysts and the products can be separated via simple phase separation, and the reactivity/stereoselectivity of the catalysts can be retained for at least three reaction cycles.     

Hydrogenation of CO2 into hydrocarbons over bifunctional system Cu–ZnO/Al2O3 + HZSM-5: Effect of proximity between the acidic and methanol synthesis sites

A one-step CO₂ hydrogenation reaction into hydrocarbons (HC) using a bifunctional system constituted by a methanol synthesis catalyst [Cu–ZnO–Al₂O₃ (CZA)] and a zeolite (HZSM-5) has been studied. The influence of the catalyst bed configuration on activity, selectivity, and HC yield has been evaluated. The results obtained at T_R = 623 K, P_R = 3.0 MPa and WHSV = 6000 h⁻¹ show that CO₂ hydrogenation and hydrocarbon selectivity were strongly influenced by the proximity between oxide and zeolite, whatever the disposition of the two catalytic active sites. Indeed, the highest conversion and the best yield of hydrocarbons (mainly C₂) were obtained with the M1 bifunctional catalysts in which the oxide–zeolite proximity is the lowest. This is ascribed to the hydrogen spillover phenomenon, which does not promote the carbon chain growth.     

Hydrogénation du CO2 en hydrocarbures sur des catalyseurs bifonctionnels CFA-HZSM-5

The increase of the concentration of greenhouse gases in the atmosphere, especially CO₂, produced mainly by the burning of fossil fuels is one of the principal causes of global warming. The transformation of CO₂ into tangible products such as fuels and/or raw materials for the petrochemical industry (methanol, hydrocarbons) is one of the possible routes. The synthesis of hydrocarbons by hydrogenation of CO₂ can be done in a single step using oxide/zeolite catalysts. The objective of our study was to evaluate the effect of the addition of zeolite and the proximity between the two oxide–zeolite sites where the oxide layer is iron-based and wherein the zeolite is represented by the HZSM-5. For this, a series of hybrid catalysts was prepared by CuO–Fe₂O₃–Al₂O₃/HZSM-5 mechanical mixing. The catalytic conversion of CO₂ has been carried out in a fixed-bed reactor under the following operating conditions: T = 350 °C, P = 30 bar, H₂/CO₂ = 3. The results show that the addition of the zeolite by intimately mixing it does not improve the catalytic properties and that the yield of hydrocarbons is best obtained with the CuO–Fe₂O₃–Al₂O₃ oxide catalyst according to the Fisher–Tropsch process (FT). However, the increase in near-zeolite oxide inhibits the formation of hydrocarbons and promotes the formation of carbon monoxide.     

Hydrodechlorination of CCl4 over carbon-supported palladium–gold catalysts prepared by the reverse “water-in-oil” microemulsion method

Two series of carbon-supported Pd–Au catalysts were prepared by the reverse “water-in-oil, W/O” method, characterized by various techniques and investigated in the reaction of tetrachloromethane with hydrogen at 423 K. The synthesized nanoparticles were reasonably monodispersed having an average diameter of 4–6 nm (Pd/C and Pd–Au/C) and 9 nm (Au/C). Monometallic palladium catalysts quickly deactivated during the hydrodehalogenation of CCl₄. Palladium–gold catalysts with molar ratio Pd:Au = 90:10 and 85:15 were stable and much more active than the monometallic palladium and Au-richer Pd–Au catalysts. The selectivity toward chlorine-free hydrocarbons (especially for C₂₊ hydrocarbons) was increased upon introducing small amounts of gold to palladium. Simultaneously, for the most active Pd–Au catalysts, the selectivity for undesired dimers C₂H_xCl_y, which are considered as coke precursors, was much lower than for monometallic Pd catalysts. Reasons for synergistic effects are discussed. During CCl₄ hydrodechlorination the Pd/C and Pd–Au/C catalysts were subjected to bulk carbiding.     

Enhanced effect of plasma on catalytic reduction of CO_2 to CO with hydrogen over Au/CeO_2 at low temperature

In terms of the reaction of CO_2 reduction to CO with hydrogen, CO_2 conversion is very low at low temperature due to the limitation of thermodynamic equilibrium(TE). To overcome this limitation, plasma catalytic reduction of CO_2 to CO in a catalyst-filled dielectric barrier discharge(DBD) reactor is studied. An enhanced effect of plasma on the reaction over Au/CeO_2 catalysts is observed. For both the conventionally catalytic(CC) and plasma catalytic(PC, Pin= 15 W) reactions under conditions of 400 °C, H_2/CO_2= 1,200 SCCM, GHSV = 12,000 mL·g~(-1)cat·h~(-1), CO_2 conversions over Au/CeO_2 reach 15.4% and 25.5% due to the presence of Au, respectively, however, those over CeO_2 are extremely low and negligible. Moreover,CO_2 conversion over Au/CeO_2 in the PC reaction exceeds 22.4% of the TE conversion. Surface intermediate species formed on the catalyst samples during the reactions are determined by in-situ temperatureprogrammed decomposition(TPD) technique. Interestingly, it disclosed that in the PC reaction, the formation of formate intermediate is enhanced by plasma, and the acceleration by plasma in the decomposition of formate species is much greater than that in the formation of formate species on Au/CeO_2. Enhancement factor is introduced to quantify the enhanced effect of plasma. Lower reactor temperature, higher gas hourly space velocity(GHSV), and lower molar ratio of H_2/CO_2 would be associated with larger enhancement factor.     

Investigation of steam reforming of acetic acid to hydrogen over Ni–Co metal catalyst

Catalytic generation of hydrogen by steam reforming of acetic acid over a series of Ni–Co catalysts have been studied. The catalyst with the molar ratio of 0.25:1 between Ni and Co was superior to other catalysts. The effects of reaction temperature, liquid hourly space velocity (LHSV) and molar ratios of steam-to-carbon (S/C) were studied in detail over this catalyst. At T = 673 K, LHSV = 5.1 h⁻¹, S/C = 7.5:1, the catalyst exhibited the best performances. Acetic acid was converted completely to hydrogen, while H₂ selectivity reached up to 96.3% and CO₂ selectivity up to 98.1% was obtained, respectively. Ni–Co catalyst showed rather stable performances for the 70 h time-on-stream without any deactivation.     

Small Cobalt Nanoparticles Favor Reverse Water-Gas Shift Reaction Over Methanation Under CO2 Hydrogenation Conditions**

Cobalt-based catalysts are well-known to convert syngas into a variety of Fischer–Tropsch (FTS) products depending on the various reaction parameters, in particular particle size. In contrast, the reactivity of these particles has been much less investigated in the context of CO₂ hydrogenation. In that context, Surface organometallic chemistry (SOMC) was employed to synthesize highly dispersed cobalt nanoparticles (Co-NPs) with particle sizes ranging from 1.6 to 3.0 nm. These SOMC-derived Co-NPs display significantly different catalytic performances under CO₂ hydrogenation conditions: while the smallest cobalt nanoparticles (1.6 nm) catalyze mainly the reverse water-gas shift (rWGS) reaction, the larger nanoparticles (2.1–3.0 nm) favor the expected methanation activity. Operando X-ray absorption spectroscopy shows that the smaller cobalt particles are fully oxidized under CO₂ hydrogenation conditions, while the larger ones remain mostly metallic, paralleling the observed difference of catalytic performances. This fundamental shift of selectivity, away from methanation to reverse water-gas shift for the smaller nanoparticles is noteworthy and correlates with the formation of CoO under CO₂ hydrogenation conditions.     

Adsorption of CO2 and CH4 on a magnesium-based metal organic framework

A magnesium-based metal organic framework (MOF), also known as Mg-MOF-74, was successfully synthesized, characterized, and evaluated for adsorption equilibria and kinetics of CO₂ and CH₄. The Mg-MOF-74 crystals were characterized with scanning electron microscopy for crystal structure, powder X-ray diffraction for phase structure, and nitrogen adsorption for pore textural properties. Adsorption equilibrium and kinetics of CO₂ and CH₄ on the Mg-MOF-74 adsorbent were measured in a volumetric adsorption unit at 278, 298, and 318 K and pressures up to 1 bar. It was found that the Mg-MOF-74 adsorbent prepared in this work has a median pore width of 10.2 Å, a BET specific surface area of 1174 m²/g, CO₂ and CH₄ adsorption capacities of 8.61 mmol g^?1 (37.8 wt.%) and 1.05 mmol g^?1 (1.7 wt.%), respectively, at 298 K and 1 bar. Both CO₂ and CH₄ adsorption capacities are significantly higher than those of zeolite 13X under similar conditions. The pressure-dependent equilibrium selectivity of CO₂ over CH₄ (q_CO2/q_CH4) in the Mg-MOF-74 adsorbent showed a trend similar to that of zeolite 13X and the intrinsic selectivity of Mg-MOF-74 at zero adsorption loading is 283 at 298 K. The initial heats of adsorption of CO₂ and CH₄ on the Mg-MOF-74 adsorbent were found to be 73.0 and 18.5 kJ mol^?1, respectively. The adsorption kinetic measurements suggest that the diffusivities of CO₂ and CH₄ on Mg-MOF-74 were comparable to those on zeolite 13X. CH₄ showed relatively faster adsorption kinetics than CO₂ in both adsorbents. The diffusion time constants of CO₂ and CH₄ in the Mg-MOF-74 adsorbent at 298 K were estimated to be 8.11 × 10^?3 and 4.05 × 10^?2 s^?1, respectively, showing a modest kinetic selectivity of about 5 for the separation CH₄ from CO₂.     

Highly stable and selective Ru/NiFe_2O_4 catalysts for transfer hydrogenation of biomass-derived furfural to 2-methylfuran

Spinel ferrites NiFe_2O_4 supported Ru catalysts have been prepared via a simple sol–gel route and applied for converting biomass-derived furfural to 2-methylfuran. The as-prepared catalysts were characterized by thermogravimetric analysis(TG), N_2 adsorption–desorption, X-ray diffraction(XRD), scanning electronic microscopy(SEM), and X-ray photoelectron spectroscopy(XPS). Results showed that the catalysts had well-dispersed Ru active sites and large surface area for calcination temperature ranging from 300 to 500 ℃. The conversion of biomass-derived furfural into 2-methylfuran was conducted over Ru/NiFe_2O_4 through catalytic transfer hydrogenation in liquid-phase with 2-propanol as the hydrogen source. A significantly enhanced activity and increased 2-methylfuran yield have been achieved in this study. Under mild conditions(180 ℃ and 2.1 MPa N_2), the conversion of furfural exceeds 97% and 2-methylfuran yield was up to 83% over the catalyst containing 8 wt% Ru. After five repeated uses, the catalytic activity and the corresponding product yield remained almost unchanged. The excellent catalytic activity and recycling performance provide a broad prospects for various practical applications.     

Behavior of adsorbed diphenyl-sulfide on the Pd/C catalyst for o-chloronitrobenzene hydrogenation

A series of diphenyl-sulfide（Ph₂S）-immobilized Pd/C catalysts(Pd-Ph₂S_（X）/C) were prepared using the wetness-impregnation and immobilization method.Pd-Ph₂S_（x）w/C catalysts employed for the hydrogenation of o-chloronitrobenzene showed very high selectivity.The structure of Pd-Ph₂S_（x）/C with different molar ratio of ligand（x-values） was characterized by XPS and TG-DSC-MS.The results suggest a "saturated" surface ratio of Ph₂S/Pd（about 0.3） was formed on the Pd-Ph₂S_（x）/C catalysts surface.The Ph₂S immobilized on the Pd particle is quite stable,and the desorption of Ph₂S or dissociative loss of phenyl group was only found at temperatures above 500 K.The possible catalytic mechanism of the Pd-Ph₂S_（x）/C catalyst was also discussed.     

Electron beam treatment of chloroethylenes/air mixture in a flow reactor

Decomposition of chloroethylenes under electron beam irradiation in a flow reactor has been studied with different reaction environments, various initial concentrations and in the presence and absence of vaporized water. Three chlorinated ethylenes—dichloroethylene (DCE), trichloroethylene (TCE), perchloroethylene (PCE)—were used as model chlorocarbons. The degree of decomposition was 48% for DCE, 98% for TCE and 90% for PCE in air reaction environment at an initial concentration of 2000 ppm and a dose of 18–20 kGy irradiation. In the presence of water vapor (5600 ppm) decomposition of TCE was about 10% higher than in dry air. The main products were found to be CO, CO₂, HCl, dichloroacetic acid (DCAA), dichloroacetyl chloride (DCAC) and dichloroethyl ester acetic acid (DEAA). DCAA, DCAC and DEAA were identified as chloro-oxygenated hydrocarbons, which could be decomposed with CO and CO₂ production. Concentration profiles show that intermediate products and yields of CO and CO₂ decrease with decreasing number of chlorine substitutions in the initial hydrocarbons.     

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.     

Recyclable Fenton-like catalyst based on zeolite Y supported ultrafine,highly-dispersed Fe2O3 nanoparticles for removal of organics under mild conditions

The active Fenton-like catalyst, obtained by highly dispersed Fe₂O₃ nanoparticles in size of 5 nm on the surface of zeolite Y, shows the excellent degradation efficiency to phenol higher than 90% under the mild conditions of room temperature and neutral solution, and the catalyst can be easily recovered with stable catalytic activity for 8 cycles.     

RuCl3 anchored onto post-synthetic modification MIL-101(Cr)-NH2 as heterogeneous catalyst for hydrogenation of CO2 to formic acid

A series of efficient ruthenium chloride (RuCl_3)-anchored MOF catalysts,such as RuCl_3@MIL-101 (Cr)-Sal,and RuCl_3@MIL-101 (Cr)-DPPB, have been successfully synthesized by post-synthetic modification (PSM)of the terminal amino of MIL-101(Cr)-NH_2 with salicylaldehyde, 2-diphenylphosphinobenzaldehyde (DPPBde) and anchoring of Ru (Ⅲ) ions. The stronger coordination electron donor interaction between Ru (Ⅲ) ions and chelating groups in the RuCl_3@MIL-101 (Cr)-DPPB enhances its catalytic performance for CO_2 hydrogenation to formic acid. The turnover number (TON) of formic acid was up to 831 in reaction time of 2 h with dimethyl sulfoxide (DMSO) and water (H_2O) as mixed solvent, trimethylamine (Et_3N) as organic base, and PPh_3 as electronic additive.     

Exploring the morphological effect of Ni_xMg_(1-x)O catalysts on CO_2 reforming of methane

To gain deep insight into the Morphological effect of Ni_xMg_(1-x)O catalysts on the reaction of CO_2 reforming with methane, we designed and fabricated three different spatial structural Ni_xMg_(1-x)O catalysts.These Ni_xMg_(1-x)O catalysts with specific models such as rod, sheet and sphere, exhibited various activity and stability in CO_2 reforming reaction. Herein Ni_xMg_(1-x)O nanorods displayed higher catalytic activity, in which methane conversion was up to 72% and CO_2 conversion was 64% at 670°C with a space velocity of 79,200 mL/(gcath), compared with nanosheet and nanosphere counterparts. Furthermore, both catalysts of Ni_xMg_(1-x)O nanorod and nanosheet showed a high resistance toward coke deposition and sintering of active sites in the process of CO_2 reforming of methane.     

Excellent electrocatalytic activity of benzil for direct reduction of CO_2 as well as indirect reduction of pyridine:A kinetic view of the electrocarboxylation process

Benzil,1,2-diphenylethane-1,2-dione, was used as an excellent electrocatalyst for reduction of carbon dioxide, CO_2. The reduction overpotential of CO_2 was reduced about 900 m V in the presence of a benzil mediator. The chemical reaction of the product of the electrocatalytic reduction of CO_2,(activated CO_2,CO_2~(·-)) with pyridine at a glassy carbon electrode, GCE, surface and in an acetonitrile-But_4NClO_4 solution was investigated by cyclic voltammetry, chronoamperometry and controlled potential coulometry.By chronoamperometry, the catalytic rate constant, k, for the electron transfer between benzil and CO_2 was obtained as 8.1 ± 0.4 M~(-1)s~(-1). The results indicate that pyridine has a strong interaction with the activated CO_2. The coulometry method was used to obtain the product of the pyridine chemical reaction with CO_2~(·-). The spectral characterizations of FTIR,~1H and ~(13)C NMR of the coulometry experiment product proved that the pyridine anion radical, Py~(·-), was carboxylated by CO_2~(·-), and isonicotinic acid is the final major product.     

Syngas production from ethanol dry reforming over Rh/CeO2 catalyst

Carbon dioxide reforming of ethanol over Rh/CeO₂ catalyst was deeply investigated at different reaction temperatures of 450–700 °C and reactant ratios (CO₂/ethanol from 1 to 3) under atmospheric pressure. The obtained results indicated that Rh/CeO₂ catalyst presented a promising activity and stability for syngas production from renewable bio-ethanol instead of conventional methane. Typically, CO₂-rich conditions (CO₂/ethanol = 3) were favorable for reaction process and dynamic coke cleaning, which led to remarkably stable performance over 65 h on stream. The strong redox capacity of CeO₂ support might also accelerate CO₂ activation and prevent the carbon accumulation over the catalyst surface. Additionally, tunable H₂/CO ratios were available by changing the CO₂/ethanol ratios. The results from characterization of samples before and after catalytic tests allowed to establish the relationship between textural properties and catalytic performance.     

Impact of palladium silicide formation on the catalytic properties of Pd/SiO2 catalysts in liquid-phase semihydrogenation of phenylacetylene

In this study, palladium silicide was formed on the sol–gel derived SiO₂ supported Pd catalysts when they were prepared by ion-exchange method using Pd(NH₃)₄Cl₂ as a palladium precursor. No other palladium phases (PdO or Pd⁰) were evident after calcinations at 450 °C for 3 h. The Pd/SiO₂ catalysts with Pd silicide formation were found to exhibit superior performance than commercial SiO₂ supported ones in liquid-phase semihydrogenation of phenylacetylene. From XPS results, the binding energy of Pd 3d of palladium silicide on the Pd/SiO₂ catalyst shifted toward larger binging energy, indicating that Pd is electron deficient. This could probably result in an inhibition of a product styrene on the Pd surface and hence high styrene selectivities were obtained at high phenylacetylene conversions. The formation of Pd silicide, however, did not have much impact on specific activity of the Pd catalysts since the TOFs were quite similar among the various catalysts with or without palladium silicides if their average particle sizes were large enough. The TOFs decreased by an order of magnitude when palladium dispersion was very high and their average particle sizes were smaller than 3–5 nm.     

Fischer–Tropsch synthesis over iron catalysts with corncob-derived promoters

A sustainable strategy for Fischer–Tropsch iron catalysts is successfully achieved by embedding of synergistic promoters from a renewable resource, corncob. The iron-based catalysts, named as "corncob-driven"catalysts, are composed of iron species supported on carbon as primary active components and various minerals(K, Mg, Ca, and Si, etc.) as promoters. The corncob-driven catalysts are facilely synthesized by a one-pot hydrothermal treatment under mild conditions. The characterization results indicate that the formation of iron carbides from humboldtine is clearly enhanced and the morphology of catalyst particles tends to be more regular microspheres after adding corncob. It is observed that the optimized corncob-driven catalyst exhibits a higher conversion than without promoters' catalyst in Fischer–Tropsch synthesis(ca. 73% vs. ca. 49%). More importantly, a synergistic effect exists in multiple promoters from corncob that can enhance heavy hydrocarbons selectivity and lower CO_2 selectivity, obviously different from the catalyst with promoters from chemicals. The proposed synthesis route of corncob-driven catalysts provides new strategies for the utilization of renewable resources and elimination of environmental pollutants from chemical promoters.