Kinetics and Mechanism of the Heterogeneous Catalytic Hydrogenolysis of Chlorobenzenes and Chlorocyclohexanes

The catalytic hydrogenolysis of hexachlorobenzene and hexachlorocyclohexanes (isomer mixture) on a nickel–chromia catalyst and hexachlorobenzene hydrogenolysis intermediates (1,2,4,5-tetrachlorobenzene, 1,2,4-trichlorobenzene, 1,2-dichlorobenzene, and chlorobenzene) are studied. The hydrogenation of an aromatic ring does not occur in the presence of chemisorbed chlorine atoms on the catalyst surface. A reaction mechanism for chlorobenzene hydrogenation was proposed taking into account experimental evidence that, in the presence of chemisorbed chlorine on the catalyst surface, hydrogen in a dissociated state is firmly bound to the surface. It is found that the desorption of the resulting hydrogen chloride is the slowest step in chlorobenzene hydrogenolysis. The hydrogenolysis of hexachlorocyclohexanes occurs via a dehydrochlorination stage with the formation of trichlorobenzenes, which are subsequently converted into chlorobenzene and benzene.     

Reduction of carbon dioxide by hydrogen on metal–carbon catalysts under supercritical conditions

The reduction of carbon dioxide with hydrogen on metal–carbon (Ru, Rh, Ir) catalysts is investigated under supercritical conditions for the first time. High selectivity (close to 100%) toward methanation with good stability of catalytic activity is observed for Ru- and Rh-containing catalyst, while the preferred reduction to CO is observed for Ir/C catalyst.     

Catalytic synthesis of nanosized feathery carbon structures via the carbide cycle mechanism

The morphology of carbon nanostructures obtained by 1,2-dichloroethane decomposition on the 90% Ni/Al₂O₃ catalyst under different reaction conditions was studied by high-resolution transmission electron microscopy. A new carbon product was discovered, which received the name of feathery carbon. The product has an extremely loose disordered structure consisting of separate fragments of a graphite-like phase. The structural disordering is assumed to be caused by the variation of chlorohydrocarbon decomposition conditions on the frontal face of the metal particle. This changes the character of carbon atom diffusion from the frontal face to the backside face of the nickel particles and finally results in a feathery morphology of the carbon phase. The specific surface area of feathery carbon is 300–400 m²/g.     

Ultra-stable Ni catalysts for methane reforming by carbon dioxide

Methane reforming by carbon dioxide has been studied over ultra-stable Ni catalysts. The catalyst was characterized by XRD, IR and TEM and temperature programmed hydrogenation. The nickel–magnesia solid solution catalyst containing low nickel has shown excellent stability (>3000 h) and no carbon deposition in the methane reforming by carbon dioxide. It was also found that the small nickel metal particle interaction with support surface is effective for the inhibition of carbon formation.     

Low temperature methanation of CO2 over an amorphous cobalt-based catalyst

CO₂ methanation is an important reaction in CO₂ valorization. Because of the high kinetic barriers, the reaction usually needs to proceed at higher temperature (>300 °C). High-efficiency CO₂ methanation at low temperature (<200 °C) is an interesting topic, and only several noble metal catalysts were reported to achieve this goal. Currently, design of cheap metal catalysts that can effectively accelerate this reaction at low temperature is still a challenge. In this work, we found that the amorphous Co–Zr_0.1–B–O catalyst could catalyze the reaction at above 140 °C. The activity of the catalyst at 180 °C reached 10.7 mmol_CO2 g_cat⁻¹ h⁻¹, which is comparable to or even higher than that of some noble metal catalysts under similar conditions. The Zr promoter in this work had the highest promoting factor to date among the catalysts for CO₂ methanation. As far as we know, this is the first report of an amorphous transition metal catalyst that could effectively accelerate CO₂ methanation. The outstanding performance of the catalyst could be ascribed to two aspects. The amorphous nature of the catalyst offered abundant surface defects and intrinsic active sites. On the other hand, the Zr promoter could enlarge the surface area of the catalyst, enrich the Co atoms on the catalyst surface, and tune the valence state of the atoms at the catalyst surface. The reaction mechanism was proposed based on the control experiments.

It is discovered that an amorphous transition metal catalyst Co–Zr0.1–B–O could effectively accelerate CO2 methanation, at a rate that is comparable to or even higher than that of some noble metal catalysts under similar conditions.     

Catalytic dehydrogenation of chloroethylbenzene

Summary In the dehydrogenation of chloroethylbenzene over a mixed oxide catalyst in presence of water vapor at 600° at space velocities of 0.2–0.35 h^–1 up to 36% of chlorostyrene is formed (yield based on the amount of chloroethylbenzene passed). In the treatment of chlorobenzene in presence of water under the same conditions the chlorine is retained in the nucleus, but when hydrogen is the diluent there is considerable breakdown of the chlorobenzene (50%) with formation of benzene and hydrogen chloride.     

Removal of CO from reformed fuels by selective methanation over Ni-B-Zr-Oδ catalysts

The Ni-B-Oδ andNi-B-Zr-Oδ catalysts were prepared by the method of chemical reduction, and the deep removal of CO by selective methanation from the reformed fuels was performed over the as-prepared catalysts. The results showed that zirconium strongly influenced the activity and selectivity of the Ni-B-Zr-Oδ catalysts. Over the Ni-B-Oδ catalyst, the highest CO conversion obtained was only 24.32% under the experimental conditions studied. However, over the Ni-B-Zr-Oδ catalysts, the CO methanation conversion was higher than 90% when the temperature was increased to 220 oC. Additionally, it was found that the Ni/B mole ratio also affected the performance of the Ni-B-Zr-Oδ catalysts. With the increase of the Ni/B mole ratio from 1.8 to 2.2, the CO methanation activity of the catalyst was improved. But when the Ni/B mole ratio was higher than 2.2, the performance of the catalyst for CO selective methanation decreased instead. Among all the catalysts, the Ni29B13Zr58Oδ catalyst investigated here exhibited the highest catalytic performance for the CO selective methanation, which was capable of reducing the CO outlet concentration to less than 40 ppm from the feed gases stream in the temperature range of 230–250 oC, while the CO2 conversion was kept below 8% all along. Characterization of the Ni-B-Oδ and Ni-B-Zr-Oδ catalysts was provided by XRD, SEM, DSC, and XPS.     

Catalytic coprocessing of waste plastics and petroleum residue into liquid fuel oils

Waste plastics of different types were catalytically coprocessed with petroleum residue of light Arabian crude oil in the presence of a number of catalysts. The purpose of the study was to explore effects of various conditions such as catalyst type, amount of catalyst, reaction time, pressure and temperature on the product distribution. The waste plastic studied included low-density polyethylene (LDPE), high-density polyethylene (HDPE), polystyrene (PS) and polypropylene (PP). A series of single (waster plastic with catalyst) and binary (waste plastic and residue with catalyst) reactions were carried out in an autoclave reactor under variable reaction conditions. The reaction conditions used were 1, 3 and 5 wt.% catalysts, 30–120 min reaction time, 400–430 °C reaction temperature and 500–1200 psi hydrogen pressure. The product distribution achieved for residue/plastic/catalyst system showed higher yields of liquid fuels as compared to residue/plastic system. Hydrocarbon gases were formed as well along with heavy oils, insoluble gums and coke. At the reaction conditions of 3 wt.% NiMo catalyst, 90 min reaction time, 1200 psi hydrogen gas pressure, 430 °C temperature and residue to plastic feed ratio of 3:2 (wt.) afforded maximum conversion of the plastics into liquid fuel oils.     

High catalytic activity and stability of palladium nanoparticles prepared by the laser electrodispersion method in chlorobenzene hydrodechlorination

Palladium nanoparticles deposited on thermally oxidized silicon and on the carbon support Sibunit by the laser electrodispersion method are extremely active in the gas-phase hydrodechlorination of chlorobenzene at 100–200°C. High conversion of chlorobenzene (above 90%) has been achieved with catalysts with an unusually low metal content (from 10^?4 to 10^?3 wt %). The cyclohexane-to-benzene ratio in the reaction products depends on the process duration, palladium content, and support nature. According to X-ray photoelectron spectroscopy (XPS) data, palladium in the catalysts retains its metallic state over a long time under the reaction conditions. Possible causes of the high catalytic activity (10⁵ mol (mol Pd)^?1 h^?1) of the palladium nanoparticles and their stability to chlorination are discussed.     

Enhanced methane decomposition over transition metal-based tri-metallic catalysts for the production of COx free hydrogen

In this study, COx-free hydrogen production via methane decomposition was studied over Cu–Zn-promoted tri-metallic Ni–Co–Al catalysts. The catalysts have been prepared by the constant pH co-precipitation method, and the nominal Ni metal loading was fixed at 50 wt % along with other metals at 10 wt% each. The catalyst activity for methane decomposition reaction was examined in a reactor between 400 °C and 700 °C and at atmospheric pressure. Different techniques such as N₂-physisorption, X-ray diffraction, H₂-TPR SEM, TEM, ICP-MS, TGA, and Raman spectroscopy were applied to characterize the catalysts. The relation between the catalyst composition and their catalytic activity has been investigated. The controlled synthesis has resulted in a series of catalysts with a high surface area. Ni–Co–Cu–Zn–Al was the most active and productive catalyst. Various characterizations indicate that the promotional effects of Cu–Zn interaction were the critical factor in catalysts' activity and stability. Ni–Co–Cu–Zn catalyst gave the highest methane conversion of 85% at 700 °C. Zn addition improves the stability of the catalyst by retaining the active metal size during the decomposition reaction. The catalyst was active for 80 h of stability study. The rapid deactivation of the Ni–Co catalyst was due to the sintering of the catalyst at 650 °C. Moreover, carbon species accumulated during the methane decomposition reaction depend on the catalysts' composition. Zn promotes the growth of reasonably long and thin carbon nanotubes, whereas the diameter of carbon nanotubes on unpromoted catalysts was large.     

Metal-free activation of H2O2 by g-C3N4 under visible light irradiation for the degradation of organic pollutants

Semiconducting carbon nitride materials were successfully prepared via a thermal poly-condensation of dicyandiamide as a precursor at >500 °C. The resulting materials were investigated as metal-free catalysts for the activation of H(2)O(2) with visible light under mild conditions, using the decomposition of Rhodamine B (RhB) in aqueous solution as a model reaction. Results revealed that carbon nitride catalysts can activate H(2)O(2) to generate reactive oxy-radicals under visible light irradiation without employment of any metal additives, leading to the mineralization of the dye. Factors affecting the degradation of organic compounds are pH values and the concentration of H(2)O(2). Recycling of the catalyst indicated no obvious deactivation during the entire catalytic reaction, indicating good (photo)chemical stability of metal-free polymeric carbon nitride photocatalysts for environmental purification. This study demonstrated a promising approach for the activation of green oxidant, hydrogen peroxide, by the newly-developed polymer photocatalysts for environmental remediation and oxidation catalysis.     

MoP/Al2O3 as a novel catalyst for sulfur‐resistant methanation

We reported γ‐alumina supported molybdenum phosphide (MoP) catalysts as a novel catalyst for sulfur‐resistant methanation reaction. The precursors of the catalyst were prepared by impregnation method and the effect of reduction temperatures (550 °C, 600 °C, 650 °C) of the precursors for sulfur‐resistant methanation was examined. The results indicated catalyst obtained by lower reduction temperature delivered better sulfur‐resistant methanation performance. Meanwhile, the influence of H₂/CO ratios and H₂S content was also investigated. The results indicated that high H₂/CO ratio and low H₂S content was favorable for methanation of MoP catalysts. The catalysts were characterized by N₂ adsorption–desorption, XRD, XPS and TEM. The results confirmed that the MoP phase was formed on all the catalysts and the physicochemical properties of the samples influenced the performance for sulfur‐resistant methanation.     

Production of hydrogen peroxide from carbon monoxide, water and oxygen over alumina-supported Ni catalysts

Novel amorphous Ni–B catalysts supported on alumina have been developed for the production of hydrogen peroxide from carbon monoxide, water and oxygen. The experimental investigation confirmed that the promoter/Ni ratio and the preparation conditions have a significant effect on the activity and lifetime of the catalyst. Among all the catalysts tested, the Ni–La–B/γ-Al₂O₃ catalyst with a 1:15 atomic ratio of La/Ni, dried at 120 °C, shows the best activity and lifetime for the production of hydrogen peroxide. The deactivation of the alumina-supported Ni–B amorphous catalyst was also studied. According to the characterizations of the fresh and used catalysts by SEM, XRD and XPS, no sintering of the active component and crystallization of the amorphous species were observed. However, it is water poisoning that leads to the deactivation of the catalyst. The catalyst characterization demonstrated that the active component had changed (i.e., amorphous NiO to amorphous Ni(OH)₂) and then salt was formed in the reaction conditions. Water promoted the deactivation because the surface transformation of the active Ni species was accelerated by forming Ni(OH)₂ in the presence of water. The formed Ni(OH)₂ would partially change to Ni₃(PO₄)₂.     

Impact of the urea–matrix combustion method on the HDS performance of Ni-MoS2/γ-Al2O3 catalysts

A detailed study has been made of the different steps involved upon the preparation of γ-Al₂O₃-supported Ni-Mo HDS catalyst precursors by urea–matrix combustion (UMxC) method. Catalyst performance was evaluated using a tubular fixed-bed reactor and the hydrodesulfurization of thiophene under normal pressure as a model reaction. The oxidic and sulfurized states of the HDS catalysts were characterized by X-ray diffraction (XRD), laser Raman spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and high resolution transmission electron microscopy (HRTEM) in order to correlate their oxidic and sulfurized properties with the catalytic behaviour. During the UMxC process several consecutive stages such as melting, dissolution and chemical reactions occurred. There was no evidence of residual carbon and well-dispersed Ni- and Mo-oxo-species supported on alumina were formed.

Urea employed as fuel not only increases the combustion rate, but also undergoes a decomposition process (endothermic reaction) that could contribute to the reduction of the combustion temperature. The urea–matrix combustion method permit to synthesize highly active γ-Al₂O₃-supported Ni-Mo HDS catalysts with a comparable promoter effect than that of corresponding catalyst prepared by impregnation method. In addition, an opposite relation between the activity and the hydrogenation properties was observed indicating that highly active HDS catalyst requires low consumption of hydrogen. Finally, both the ignition temperature and the urea-oxidizer ratio produce no significant changes in the HDS catalytic properties of Ni-Mo-based catalysts.     

沉淀剂对镍基甲烷化催化剂性能的影响

利用尿素、碳酸铵、氨水三种沉淀剂制备了不同的镍基甲烷化催化剂,考察了沉淀条件对催化剂性能的影响。通过XRD、H₂-TPR、BET、TPO等方法对催化剂进行表征。结果表明,使用不同沉淀剂所得催化剂性能各不相同。采用尿素沉淀剂,颗粒的比表面积达到了223.55m²/g,具有较稳定的催化活性;碳酸铵沉淀颗粒粒径较大,分散也不够均匀,催化剂更容易积炭;氨水沉淀制备的催化剂粒径小,与载体结合性强,高温下活性组分易于流失。分析认为,沉淀剂影响了催化剂前驱体的形态和结构,造成了分散度、晶相结构、对氢的吸附性质以及抗积炭性等多方面的差异,表现出甲烷化反应活性和稳定性的不同。     

Catalytic synthesis of C-alkylimidazoles over platinum-alumina catalysts

The synthesis of C-alkylimidazoles from 1,2-diamines and carboxylic acids over bifunctional platinum—alumina catalysts has been studied. It has been shown that this method is effective for the synthesis of 2-alkyl and 2,4-dialkylimidazoles including imidazoles with long-chain alkyls. The effect of the reaction temperature, space velocity of the flow of the raw materials, and dilution by hydrogen on the yield of product has been examined for the example of the synthesis of 2-methylimidazole from ethylenediamine and acetic acid, and the stability of the catalyst in continuous reaction cycles with intermediate oxidative regeneration has been studied. The composition of the accompanying products has been established and a mechanism proposed for their formation.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, Moscow 117913. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 4, pp. 932–940, April, 1992.     

Excess volumes of chlorobenzene and bromobenzene with some chloroethanes at 303.15 and 313.15 K

Volume changes on mixing for the binary systems formed by chlorobenzene with 1,2-dichloroethane, 1,1,1-trichloroethane and 1,1,2,2-tetrachloroethane, and by bromobenzene with 1,2-dichloroethane, 1,1,1-trichloroethane and 1,1,2,2-tetrachloroethane, have been measured as functions of composition at 303.15 and 313.15 K. The measured excess volumes are positive over the entire range of composition for the binary systems chlorobenzene + 1,2-dichloroethane and bromobenzene + 1,2-dichloroethane at 303.15 K, and for chlorobenzene + 1,1,2,2-tetrachloroethane at 313.15 K. The measured volumes V^E are negative over the entire composition range for the remaining systems, except for the system chlorobenzene + 1,1,2,2-tetrachloroethane at 303.15 K, where an inversion of the sign of V^E is observed over part of the concentration range.     

Decomposition of methane over alumina supported Fe and Ni–Fe bimetallic catalyst: Effect of preparation procedure and calcination temperature

Catalytic decomposition of methane has been studied extensively as the production of hydrogen and formation of carbon nanotube is proven crucial from the scientific and technological point of view. In that context, variation of catalyst preparation procedure, calcination temperature and use of promoters could significantly alter the methane conversion, hydrogen yield and morphology of carbon nanotubes formed after the reaction. In this work, Ni promoted and unpromoted Fe/Al₂O₃ catalysts have been prepared by impregnation, sol–gel and co-precipitation method with calcination at two different temperatures. The catalysts were characterized by X-ray diffraction (XRD), N₂ physisorption, temperature programmed reduction (TPR) and thermogravimetric analysis (TGA) techniques. The catalytic activity was tested for methane decomposition reaction. The catalytic activity was high when calcined at 500 °C temperature irrespective of the preparation method. However while calcined at high temperature the catalyst prepared by impregnation method showed a high activity. It is found from XRD and TPR characterization that disordered iron oxides supported on alumina play an important role for dissociative chemisorptions of methane generating molecular hydrogen. The transmission electron microscope technique results of the spent catalysts showed the formation of carbon nanotube which is having length of 32–34 nm. The Fe nanoparticles are present on the tip of the carbon nanotube and nanotube grows by contraction–elongation mechanism. Among three different methodologies impregnation method was more effective to generate adequate active sites in the catalyst surface. The Ni promotion enhances the reducibility of Fe/Al₂O₃ oxides showing a higher catalytic activity. The catalyst is stable up to six hours on stream as observed in the activity results.     

磷钨杂多酸盐催化的氯丙烯水油两相条件下的环氧化

研究了磷钨杂多酸盐对氯丙烯与H2O2水溶液两相条件下环氧化反应的催化活性.反应结果表明,环氧氯丙烷的产率受溶剂二氯乙烷量影响;二氯乙烷作溶剂时,这一反应体系具有很好的催化性能,环氧氯丙烷产率可达88.3%;甲苯不是氯丙烯环氧化的优良溶剂.     

Carbon nanofiber supported palladium catalyst for liquid-phase reactions: An active and selective catalyst for hydrogenation of cinnamaldehyde into hydrocinnamaldehyde

Carbon nanofibers (CNFs) prepared by decomposition of ethane over a Ni/alumina catalyst, are used as support for palladium clusters. The carbon support displays a mean diameter of 40–50 nm, lengths up to several tens of micrometers, as highlighted by transmission electron microscopy (TEM) observations and a specific surface area of about 50 m²/g. The spheroidal palladium particles have a relatively homogeneous and sharp size distribution, centered at around 4 nm. This novel Pd/carbon nanofiber catalyst displays unusual catalytic properties and is successfully used in the selective hydrogenation of the C=C bond in cinnamaldehyde at a reaction temperature of around 80°C, under continuous hydrogen flowing at atmospheric pressure. The high performances of this novel catalyst in terms of efficiency and selectivity are, respectively, related to the inhibition of the mass-transfer processes over this non-porous material and to peculiar palladium–carbon interactions. It is concluded that the absence of microporosity in the carbon nanofibers favours both the high activity and selectivity which is confirmed by comparison with the commercially available high surface area charcoal supported palladium catalyst.