Carbon dioxide hydrogenation over nickel-, ruthenium-, and copper-based catalysts: Review of kinetics and mechanism

This study critically reviews the mechanism of CO₂ hydrogenation over Ni, Ru, and Cu, and the effect of catalyst properties and operating conditions on reaction kinetics. Most studies have reported the presence of CO and formate species on Ni-, Ru-, and Cu-based catalysts, where subsequent conversion of these species depends on the type of catalyst and the physicochemical properties of the catalyst support. Methane is the major product that forms during CO₂ hydrogenation over Ni and Ru catalysts, while methanol and CO are mainly produced on Cu catalysts. A different approach for catalyst formulations and/or process development is required where long chain hydrocarbons are desired.     

Vapor-phase selective hydrogenation of maleic anhydride to succinic anhydride over Ni/TiO2 catalysts

A series of supported Ni/TiO₂ catalysts were prepared by incipient wetness impregnation method under different calcination temperatures, and the as-prepared catalysts were characterized by X-ray diffraction (XRD), hydrogen temperature-programmed reduction (H₂-TPR) and X-ray photoelectron spectroscopy (XPS). The catalytic properties of these Ni/TiO₂ catalysts were investigated in the vapor phase hydrogenation of maleic anhydride (MA) to succinic anhydride (SA). The results showed that the catalytic activity and the selectivity of the Ni/TiO₂ catalysts were strongly affected by the calcination temperature. The catalyst calcined at 1023 K showed a relatively higher SA selectivity of 96% at high MA conversion (96%) under the tested conditions (493 K and 0.2 MPa). The improvement of SA selectivity could be mainly assigned to the presence of suitable metal–support interaction, which can play a role in catalytic property of active nickel species as electron promoter. Besides, the change of surface properties of TiO₂ support with the increasing calcination temperatures, e.g., the decrease of Lewis acid sites, might also have some positive role in reducing the side-products like γ-butyrolacetone (GBL).     

Ionic liquid as an efficient promoting medium for synthesis of dimethyl carbonate by oxidative carbonylation of methanol

The synthesis of dimethyl carbonate by oxidative carbonylation of methanol using Cu salt catalysts in the presence of various room temperature ionic liquids (RTILs) was reported. Among the ionic liquids used, N-butylpyridinium tetrafluoroborate was the most effective promoter in terms of the conversion of methanol and the selectivity to dimethyl carbonate (DMC). The influences of reaction temperature, pressure, time, molar ratio of CO/O₂, and amount of the ionic liquid on the oxidative carbonylation of methanol were investigated. The results indicated that under the reaction conditions of 120 °C and 2.4 MPa of a 2:1 mixture of CO and O₂, 17.2% conversion of methanol, 97.8% selectivity of DMC and a DMC productivity of 4.6 g g⁻¹ cat h⁻¹ were achieved. The N-butylpyridinium tetrafluoroborate-meditated CuCl catalyst system could be reused at least five recycles with the same selectivity and a slight loss of catalytic activity due to loss of the catalyst during handling and transferring the reaction mixture.     

载体制备方法对Ni/ZrO_2催化剂顺酐液相加氢性能的影响

分别以水和甲醇为溶剂制备晶粒尺寸基本一致的四方相ZrO_2,通过浸渍法制备Ni质量分数10%的Ni/ZrO_2-W(水为溶剂)与Ni/ZrO_2-M(甲醇为溶剂)催化剂,考察其催化顺酐液相加氢性能。采用BET、XRD、H_2-TPR、H_2-TPD和in situ FT-IR对催化剂进行表征。结果表明,以甲醇为溶剂制备的ZrO_2比表面积明显小于以水为溶剂制备的ZrO_2,但Ni/ZrO_2-M催化剂存在强的金属-载体相互作用,其活性金属分散度以及C=O加氢活性明显高于Ni/ZrO_2-W催化剂。在反应温度210℃和氢压5 MPa条件下反应3 h,Ni/ZrO_2-M催化剂上顺酐转化率几乎100%,γ-丁内酯选择性为22.8%,Ni/ZrO_2-W催化剂上γ-丁内酯选择性仅为2.5%。     

Influence of Preparation Modes on Pt–Ni/CNTs Catalysts Used in the Selective Hydrogenation of Cinnamaldehyde to Hydrocinnamaldehyde

Pt–Ni/CNTs catalysts are prepared by different impregnation techniques and different reduction methods (H₂, HCHO, and KBH₄) for the selective hydrogenation of cinnamaldehyde (CMA) to hydrocinnamaldehyde (HCMA) and investigated by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and temperature programmed reduction (H₂-TPR) techniques. The results show that the catalytic selectivity and activity of the Pt–Ni/CNTs catalysts would significantly be improved by using KBH₄ as a reducing agent, due to the electronic synergetic effect of Pt–Ni–B, and 96% for conversion of CMA and 88% for selectivity of HCMA are obtained over Pt–Ni/CNTs catalyst reduced by KBH₄. Furthermore, the hydrogenation rate of CMA and selectivity of CMA to HCMA over Pt–Ni/CNTs catalyst are significantly improved in the presence of trace base or acid promoters again. The best result (92% for conversion of CMA and 96% for selectivity of HCMA) is obtained when NaOAc is used as base promoter.     

Amorphous unsupported Ni–Mo sulfide prepared by one step hydrothermal method for phenol hydrodeoxygenation

Unsupported sulfide catalysts are a potentially promising approach towards furthering the understanding and development of a better heterogeneous catalytic system capable of performing the hydrodeoxygenation (HDO) of bio-oil proficiently under mild and short reaction conditions and times, respectively. Amorphous unsupported Ni–Mo sulfide, prepared from ammonium tetrathiomolybdate (ATTM) by a one step hydrothermal method, is already sulfided and so does not need a sulfidation step. The addition of the Ni promoter prevents the growth of Mo sulfide particles and causes a reduction in the surface area and a change in the pore characteristics as the amount of added Ni was increased. Ni sulfide alone (no Mo) showed a completely different morphology and properties compared to those of the Mo-containing sulfides, with or without the copresence of Ni. The activity and selectivity of catalysts was investigated using phenol as a model substrate in the direct-deoxygenation (DDO) and hydrogenation (HYD) reactions in a HDO system. The Ni–Mo sulfide catalyst with optimal Ni amount had a significantly higher phenol conversion efficiency (96.2 mol%), and favored a HYD pathway, than that seen for the Mo sulfide one (71.0 mol%) that favored a DDO pathway. H₂-temperature programmed desorption (TPD) suggested that this synergy was mainly derived from a change in the quality and not the number of the active sites. The synergetic effect was a function of the stoichiometric composition with the maximum synergetic effect being obtained at a Ni/(Mo + Ni) ratio of 0.3. This could result from the high dispersion of the active species and the generation of a more active Ni–Mo–S phase.     

Gas phase hydrogenation of ortho-chloronitrobenzene (O-CNB) to ortho-chloroaniline (O-CAN) over unpromoted and alkali metal promoted-alumina supported palladium catalysts

A series of alkali metals (Li, Na, K and Cs) promoted alumina-supported palladium catalysts were prepared by a wet impregnation method and characterized by X-ray diffraction (XRD) and CO chemisorption measurements. The samples were tested for the gas phase hydrogenation of ortho-chloronitrobenzene (O-CNB) to ortho-chloroaniline (O-CAN) in a fixed-bed micro reactor at 250 °C under normal atmospheric pressure. The promoted-Pd/Al₂O₃ catalysts show higher conversion for O-CNB and the hydrogenation activity of O-CNB per site decreases with the increasing ionic radius of the alkali metal promoter ions. However, the selectivity for O-CAN remains more or less the same in both unpromoted and promoted catalysts and also irrespective of the nature of the alkali metal promoter ions used for promotion of alumina support. Despite, similar activity and selectivity observed between Li- and Na-promoted Pd/Al₂O₃ catalysts, the Na-promoted showed higher resistance for coke formation than a Li-promoted catalyst. The increase in the intrinsic activity of palladium site on alkali promotion has been attributed to the increase in hydrogenation activity over promoted catalysts.     

Study on an iron–manganese Fischer–Tropsch synthesis catalyst prepared from ferrous sulfate

A systematic study was undertaken to investigate the effects of the initial oxidation degree of iron on the bulk phase composition and reduction/carburization behaviors of a Fe–Mn–K/SiO₂ catalyst prepared from ferrous sulfate. The catalyst samples were characterized by powder X-ray diffraction (XRD), Mössbauer spectroscopy, X-ray photoelectron spectroscopy (XPS) and H₂ (or CO) temperature-programmed reduction (TPR). The Fischer–Tropsch synthesis (FTS) performance of the catalysts was studied in a slurry-phase continuously stirred tank reactor (CSTR). The characterization results indicated that the fresh catalysts are mainly composed of α-Fe₂O₃ and Fe₃O₄, and the crystallite size of iron oxides is decreased with the increase of the initial oxidation degree of iron. The catalyst with high content of α-Fe₂O₃ in its as-prepared state has high content of iron carbides after being reduced in syngas. However, the catalyst with high content of Fe₃O₄ in its as-prepared state cannot be easily carburized in CO and syngas. FTS reaction study indicates that Fe-05 (Fe³⁺/Fe_total = 1.0) has the highest CO conversion, whereas Fe-03 (Fe³⁺/Fe_total = 0.55) has the lowest activity. The catalyst with high CO conversion has a high selectivity to gaseous hydrocarbons (C₁–C₄) and low selectivity to heavy hydrocarbons (C₅₊).     

Selective production of methanol from syngas over LaTi1−xCuxO3 mixed oxides

Carbon monoxide hydrogenation was studied over partially substituted copper-containing LaTi_1–xCu_xO₃ oxides and on copper supported on La₂O₃. The unsubstituted (x = 0) oxide was weakly active for CO hydrogenation, whereas all the other oxides were more active and exhibited high selectivity to methanol. Particularly, for substitutions x = 0.5–0.6, where the perovskite structure was observed, CO conversions close to 22% and selectivity close to 80% were found. Cu/La₂O₃ was, however, less active and yielded CO₂ and hydrocarbons as the major products. Using X-ray photoelectron spectroscopy it was determined that under reaction conditions copper exists as reduced species. The L₃VV X-ray induced Auger transition at 1849.2 eV observed for a representative LaMn_0.5Cu_0.5O₃ catalyst prereduced and used in CO hydrogenation at 573 K, suggests that Cu⁺ species dominates in spent catalyst. These Cu⁺ species are believed to be stable under reaction conditions in the perovskite structure, only a slight Cu enrichment occurs on the topmost layer of catalysts.     

Development of cobalt–copper nanoparticles as catalysts for higher alcohol synthesis from syngas

The synthesis of higher alcohols from syngas has been studied over different types of Cu-based catalysts. In order to provide control over the catalyst composition at the scale of a few nanometers, we have synthesized two sets of Co–Cu nanoparticles with novel structures by wet chemical methods, namely, (a) cobalt core–copper shell (Co@Cu) and (b) cobalt–copper mixed (synthesized by simultaneous reduction of metal precursors) nanoparticles. These catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and temperature programmed reduction (TPR). The catalysts were tested for CO hydrogenation at temperatures ranging from 230 °C to 300 °C, 20 bar and 18,000 scc/(hr.gcat). It was observed that the Co–Cu mixed nanoparticles with higher Cu concentration exhibit a greater selectivity towards ethanol and C₂₊ oxygenates. The highest ethanol selectivity achieved was 11.4% with corresponding methane selectivity of 17.2% at 270 °C and 20 bar.     

Highly dispersed and confined Ni/MMO catalyst synthesized in a rotating packed bed for hydrogenation of maleic anhydride

Catalytic hydrogenation of maleic anhydride (MA) into succinic anhydride (SA) is one of the most important transformations in synthetic organic chemistry. Herein, we firstly synthesized well-dispersed nickel particles confined by mixed metal oxides (Ni/MMO) derived from in situ transformation of Ni-Al hydrotalcite in a rotating packed bed (RPB) to catalyze this process. A series of Ni/MMO catalysts (63 wt%–89 wt% Ni) were effectively fabricated and the structure–activity relationship was established. Results showed that a Ni/MMO catalyst (82 wt% Ni) with substantial surface defect sites and the highest Ni surface area among the prepared Ni/MMO catalysts, demonstrates the highest activity with ~100% MA conversion and ~100% selectivity to SA under 25°C within 77 min. This is, to our knowledge, the highest conversion and selectivity under room temperature to date. Moreover, the Ni/MMO catalyst prepared by RPB has higher specific surface area and Ni surface area, therefore possessing a higher hydrogenation rate compared to that by stirred tank reactor (1.69 vs. 1.36, 10⁻³·mol_MA/g_cat/min). These results will provide an attractive option of the catalysts for MA hydrogenation, and a novel strategy for synthesizing nickel catalyst derived from Ni-Al hydrotalcite.     

Effect of Li Promoter on titania-supported Rh catalyst for ethanol formation from CO hydrogenation

The addition of 0.10 wt% Li to Rh/TiO₂ more than doubled the CO conversion for CO hydrogenation while increasing ethanol selectivity. The addition of Li also increases formation of C₂ oxygenates at the expense of C₁ species, methanol and methane. This is attributed to enhanced dispersion of Rh by Li that appears to reduce dissociation of CO, which previous studies have shown requires large ensembles of Rh atoms on the surface. Li promotion appears to increase the associatively adsorbed CO, allowing for increased H₂ chemisorption on the surface compared to the dissociative adsorption of the same number of CO atoms. This increases selectivity to ethanol compared to the unpromoted catalysts. CO-TPD shows more reactive adsorbed CO species on the Li-promoted catalyst. FTIR results suggest that Li promotion alters CO bonding at bridged or interfacial sites and its effect is more structural than electronic.     

Effect of impregnation sequence on performance of SiO2 supported Cu-Fe catalysts for higher alcohols synthesis from syngas

The effects of different impregnation sequences of copper and iron on the performance of Cu-Fe/SiO₂ catalysts for higher alcohols synthesis from syngas were investigated by N₂ adsorption, XRD, H₂-TPR, CO-IR, XPS, and CO hydrogenation reaction. The results indicate that the catalyst prepared by impregnation of support first with Fe and then with Cu exhibits the highest selectivity (36.1%) and space time yield (153.3 g·kg_cat^− 1·h^− 1) of alcohols. The CO conversion and alcohol selectivity of the catalysts was closely related to the content of surface Cu, and the ratio of surface contents of Cu to Fe, respectively.     

High selective production of tetrahydrofurfuryl alcohol: Catalytic hydrogenation of furfural and furfuryl alcohol

Tetrahydrofurfuryl alcohol could be obtained by catalytic hydrogenation of either furfural or furfuryl alcohol using Pd-, Ru-, Rh- and Ni-supported catalysts as well as their mixtures with a Cu-supported catalyst. In the case of furfural hydrogenation, the best results (97 % yield, 100 % conversion, 98 % selectivity) were obtained in the presence of Ni and Cu. However, this catalytic mixture could not be recycled. In the case of furfuryl alcohol hydrogenation, Ni-supported catalysts were the most active. Nickel-onsilica-alumina catalyst containing 59 % of metal lead to the best results (98–99 % yield, selectivity and conversion >99 %). Moreover, it could be recycled. Hydrogenation of furfuryl alcohol in the presence of this catalyst was the best procedure for the production of tetrahydrofurfuryl alcohol.     

Synthesis of AlOOH slurry catalyst and catalytic activity for methanol dehydration to dimethyl ether

AlOOH slurry catalysts were prepared by complete liquid-phase technology from aluminum iso-propoxide (AIP). Dehydration of methanol to dimethyl ether (DME) over these catalysts was investigated in slurry reactor. The catalysts were characterized by X-ray diffraction (XRD), nitrogen adsorption, temperature-programmed desorption of ammonia (NH₃–TPD). The results showed that the slurry catalysts had high specific surface area and pore volume, and the specific surface area and the strength of weak acidic sites were influenced considerably by the molar ratio of H₂O/AIP and HNO₃/AIP. Activity tests indicated that AlOOH slurry catalysts had excellent catalytic activity and stability in slurry reactor for the dehydration of methanol to dimethyl ether, and the activity correlated well with the strength of weak acidic sites of catalysts, which can be controlled by changing the H₂O/AIP and HNO₃/AIP molar ratios. The average methanol conversion at even stage reaches nearly 80% and DME selectivity almost 100% over CAT-P1 catalyst. No deactivation was found during the reaction of 500 h. It is also expected that CAT-P1 becomes a promising methanol dehydration catalyst for the STD process based on CuZuAl methanol synthesis catalyst.     

Effect of glow discharge plasma on rhodium-based catalyst for oxygenates synthesis

Rhodium-based catalysts were prepared by impregnation, treated with glow discharge plasma, characterized by X-ray diffraction, X-ray photoelectron spectroscopy, H₂ temperature-programmed reduction, H₂ temperature-programmed desorption and CO temperature-programmed desorption, and investigated for oxygenate synthesis from CO hydrogenation. Based on the characterization results, plasma treatment endowed the samples with smaller particle size, higher dispersion of active components, and an enrichment of active components on the surface as well. As a result, the reducibility and adsorption properties were modified. In catalytic tests, the catalytic activity for CO hydrogenation over the samples treated by plasma was improved remarkably: the conversion of CO and the yield of oxygenates increased at most by a factor of 78.62% and 51.96%, respectively, while the selectivity of ethanol and methanol in the oxygenates was enhanced as well. Translated from Natural Gas Chemical Industry, 2006, 31(1): 21–24 [译自: 天然气化工]     

Vapour phase hydrogenation of phenol over Pd/C catalysts: A relationship between dispersion,metal area and hydrogenation activity

A series of palladium supported on activated carbon catalysts, with Pd varying from 0.5 to 6.0 wt%, were prepared via wet impregnation method using PdCl₂ · xH₂O as a precursor salt. The dried samples were further reduced at 573 K in hydrogen and characterized by CO adsorption at room temperature in order to determine the dispersion, metal area and particle size. The catalysts were tested for vapour phase phenol hydrogenation in a fixed-bed all glass micro-reactor at a reaction temperature of 453 K under normal atmospheric pressure. The decrease in metal surface area as well as dispersion with corresponding increase in turn-over frequency (TOF) against palladium loadings suggest the unusual inverse relationship that exist between Pd dispersion and phenol hydrogenation activity over Pd/carbon catalysts. The stability of TOF at larger crystallite size indicates that phenol hydrogenation is less sensitive reaction especially beyond 3 wt% of Pd content. It is evident from the results that structural properties of the catalysts strongly influence the availability of Pd atoms on the surface for CO chemisorption and hence for phenol hydrogenation. A comparison between selectivity and product yield of the reaction against overall phenol conversion indicates that changes in reaction selectivity for cyclohexanone or cyclohexanol is independent of phenol conversion level and either of the product is not formed at the cost of another. The stability of the catalysts with reaction time suggests that coke formation on the surface of the catalyst is less significant and the formation of cyclohexanone remains almost total even at higher reaction temperatures.     

Performance of Ni/Nano-ZrO2catalysts for CO preferential methanation简

Large surface areas nano-scale zirconia was prepared by the self-assembly route and was employed as support in nickel catalysts for the CO selective methanation. The effects of Ni loading and the catalyst calcination temperature on the performance of the catalyst for CO selective methanation reaction were investigated. The cata- lysts were characterized by Brunauer-Emmett-Teller （BET）, transmission electron microscope （TEM）, X-ray dif- fraction （XRD） and temperature-programmed reduction （TPR）. The results showed that the as-synthesized Ni/nano-ZrO2 catalysts presented high activity for CO methanation due to the interaction between Ni active particle and nano zir- conia support. The selectivity for the CO methanation influenced significantly by the particle size of the active Ni species. The exorbitant calcination resulted in the conglomeration of dispersive Ni particles and led to the decrease of CO methanation selectivity. Among the catalysts studied, the 7.5% （by mass） Ni/ZrO2 catalyst calcinated at 500℃ was the most effective for the CO selective methanation. It can preferentially catalyze the CO methanation with a higher 99% conversion in the CO/CO2 competitive methanation system over the temperature range of 260-280℃, while keeping the CO2 conversion relatively low.     

Ru/γ-Fe2O3-Al2O3催化剂在磁稳定床中 苯选择性加氢性能

设计建造了磁稳定床加氢实验装置,以磁性氧化铝为载体,通过浸渍法制备了蛋壳型钌基磁性Ru/γ-Fe₂O₃-γ-Al₂O₃微球催化剂,详细考察了磁性催化剂的制备参数、磁稳定床的操作参数对苯选择性加氢的影响。结果表明磁稳定床的链式操作状态提高了环己烯的选择性,证实了所研制的蛋壳型钌基磁性微球催化剂适用于磁稳定床中苯的选择性加氢工艺,具有较好的应用前景。     

Synthesis of a nano-nickel catalyst modified by ruthenium for hydrogenation and hydrodechlorination

A nano-nickel catalyst was prepared by chemical reduction with N₂H₄·H₂O, and was modified with ruthenium by chemical replacement. The nano-Ni and NiRu catalysts were characterized by X-ray diffraction, transmission electron microscope, and X-ray photoelectron spectroscopy. The catalysts were evaluated in the liquid phase hydrogenation of cinnamaldehyde and hydrodechlorination of chlorobenzene. The NiRu catalyst exhibited a much higher selectivity to the hydrocinnamaldehyde and a better hydrodechlorination activity and stability than those of the Ni catalyst.