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.     

Promotion effect of nickel for Cu–Ni/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts in the transfer dehydrogenation of primary aliphatic alcohols

Cu–Ni/γ-Al₂O₃ bimetallic catalysts were developed for anaerobic dehydrogenation of non-activated primary aliphatic alcohols to aldehydes. Systematic investigation about the promotion effect of nickel on the catalytic performance was carried out. Hydrogenation of C=C bond rather than C=O bond, was significantly improved over Cu–Ni/γ-Al₂O₃ catalyst by introducing nickel, which interprets the good conversion of primary aliphatic alcohols. This work would contribute to design new catalysts for dehydrogenation of primary aliphatic alcohols.     

Effect of the Ni/Cu ratio on the composition and catalytic properties of nickel-copper alloy in anisole hydrodeoxygenation

The activity of NiCu-SiO₂ catalysts with a metal content of 90% and different Ni/Cu ratios has been investigated in the hydrodeoxygenation of anisole, a model compound of bio-oil, at 280°C and 6 MPa. A homogeneous phase composition of the active component has been synthesized by the co-decomposition of nickel and copper nitrates followed by the introduction of SiO₂ as a stabilizer. The resulting catalysts have been characterized by temperature-programmed reduction, X-ray powder diffraction, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy combined with energy-dispersive microanalysis. The bulk and surface composition of active-component particles has been determined by XPS and X-ray diffraction. In all of the catalysts containing 15–85 wt % Ni, there are two types of solid solutions. One has a constant composition, Cu_0.95Ni_0.05, which is independent of the Ni/Cu ratio in the catalyst; in the other, the nickel stoichiometry increases with an increasing Ni content of the active component. A correlation has been established between the Ni/Cu ratio and the rate constants of the reaction examined and between the Ni/Cu ratio and the degree of hydrodeoxygenation for all samples. The most active catalyst is Ni85Cu5-SiO₂.     

Effect of pressure on the efficiency of nickel and nickel-copper catalysts in decomposition of methane

Methane decomposition into hydrogen and nanofibrous carbon in the presence of high-percentage catalysts (70–90)% Ni–(0–20)% Cu–10% Al at a temperature of 948 K and pressures of 1 to 5 atm was studied in order to develop a technology for enrichment of natural gas with hydrogen. It was found that, With an increasing copper content in the catalyst and and with increasing pressure, the average, methane decomposition rate decreases by 10–20% and the catalyst lifetime and the specific yield of hydrogen (mol/mol_Ni+Cu) become (3.8–12) times higher over the catalyst deactivation period. The mechanisms by which the pressure and the copper content of the catalyst affect these process characteristics are discussed.     

甲烷部分氧化制合成气Ⅱ．镍系催化剂的反应性能

主要用第四周期金属元素的氧化物与Ａｌ２Ｏ３的复合氧化物催化剂上甲烷氧化的结果证实了催化剂设计中的预测：（１）催化剂首先应能解离活化甲烷，（２）催化剂要能较快地活化Ｏ２分子．只有同时满足这两个条件，催化剂才可能有较好的甲烷部分氧化活性．第四周期元素中只有镍具有这样的性质．Ｃｕ，Ｍｎ，Ｃｒ，Ｌａ，Ｃａ，Ｚｎ等氧化物的添加可明显提高Ｎｉ－Ａｌ２Ｏ３催化剂的甲烷部分氧化性能，其中Ｃｕ的助催化性能最好．催化剂ＮｉＯ－ＣｕＯ－Ａｌ２Ｏ３，ＮｉＯ－ＭｎＯ－Ａｌ２Ｏ３，ＮｉＯ－Ｃｒ２Ｏ３－Ａｌ２Ｏ３的反应活性和选择性顺序，与金属Ｃｕ，Ｍｎ，Ｃｒ上ＣＯ和Ｈ２脱附的顺序是一致的     

Hydrogen Production by Steam Reforming of Ethanol Over Mesoporous Ni–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–ZrO<Subscript>2</Subscript> Catalysts

This review paper reports the recent progress concerning the application of nickel–alumina–zirconia based catalysts to the ethanol steam reforming for hydrogen production. Several series of mesoporous nickel–alumina–zirconia based catalysts were prepared by an epoxide-initiated sol–gel method. The first series comprised Ni–Al₂O₃–ZrO₂ xerogel catalysts with diverse Zr/Al molar ratios. Chemical species maintained a well-dispersed state, while catalyst acidity decreased with increasing Zr/Al molar ratio. An optimal amount of Zr (Zr/Al molar ratio of 0.2) was required to achieve the highest hydrogen yield. In the second series, Ni–Al₂O₃–ZrO₂ xerogel catalysts with different Ni content were examined. Reducibility and nickel surface area of the catalysts could be modulated by changing nickel content. Ni–Al₂O₃–ZrO₂ catalyst with 15 wt% of nickel content showed the highest nickel surface area and the best catalytic performance. In the catalysts where copper was introduced as an additive (Cu–Ni–Al₂O₃–ZrO₂), it was found that nickel dispersion, nickel surface area, and ethanol adsorption capacity were enhanced at an appropriate amount of copper introduction, leading to a promising catalytic activity. Ni–Sr–Al₂O₃–ZrO₂ catalysts prepared by changing drying method were tested as well. Textural properties of Ni–Sr–Al₂O₃–ZrO₂ aerogel catalyst produced from supercritical drying were enhanced when compared to those of xerogel catalyst produced from conventional drying. Nickel dispersion and nickel surface area were higher on Ni–Sr–Al₂O₃–ZrO₂ aerogel catalyst, which led to higher hydrogen yield and catalyst stability over Ni–Sr–Al₂O₃–ZrO₂ aerogel catalyst.     

Change in carbon content on the surface of a multicomponent catalyst during its reduction, oxidation and due to action of the reaction medium

The change in the carbon content on the surface of Fe, Cu, Ni containing catalysts has been studied by X-ray Photoelectron Spectroscopy (XPS) under different treatments. It has been concluded that the superficial carbon content affects the content of an active element,e.g. copper, on the catalyst surface.     

Hydrogen production by methanol steam reforming on a cordierite monolith reactor coated with Cu–Ni/LaZnAlO<Subscript>4</Subscript> and Cu–Ni/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts

The performance of Cu–Ni/LaZnAlO₄ and Cu–Ni/γ-Al₂O₃ catalysts in the methanol reforming process in a monolith reactor in the temperature range of 200–350 °C, feed flow rate of WHSV = 20.8 h^?1 and atmospheric pressure has been investigated. In order to perform a more thorough investigation, surface area, morphology and crystalline structure of the synthetic catalysts have been studied using BET, FE-SEM, TPR, FT-IR, TEM, TGA and XRD analyses. The results have shown that Cu–Ni/LaZnAlO₄ catalyst synthesized by combustion reaction method under ultrasound irradiation has a very high efficiency and catalytic activity, low reduction temperature, high mechanical resistance and large pore sizes. The latter causes a higher percentage of active metal impregnation and better distribution on the support, greater resistance against sintering and maintenance of catalyst inertness at temperatures over 1000 °C, in comparison with conventional catalysts such as Cu–Ni/γ-Al₂O₃. This make its substitution for currently used catalysts affordable.     

一种适用于生物油低温制氢的碳纳米纤维促进的镍催化剂

氢气作为一种高热值的清洁能源广泛地应用于工业中. 研究证明: 生物质通过化学过程可以转化为多种气体燃料(氢气), 液体燃料以及高附加值的化学品. 生物质作为一种环境友好型再生洁净能源, 其研究越来越受到关注. 本文旨在探讨利用生物油为原料, 通过水蒸汽重整方法制备富氢合成气的过程. 利用均匀浸渍的方法制备了一种高分散的碳纳米纤维促进的镍(Ni/CNFs)催化剂, 并将普通的Al₂O₃作为载体的Ni/Al₂O₃催化剂和Ni/CNFs作对比. 研究了重整温度以及水蒸汽和碳摩尔比(n_S/n_C)对生物油水蒸汽重整制氢的影响. 结果表明: 碳纳米纤维作为载体用于生物油水蒸汽重整制氢的效果要远优于普通的Al₂O₃载体, 利用22% Ni/CNFs 催化剂时, 在实验温度范围内(350-550℃), 最高生物油转化率和氢气产率分别达到了94.7%和92.1%, 通过研究重整条件以及对催化剂进行表征探讨了生物油在水蒸汽重整过程中催化剂的构效关系.     

Ni基催化剂上木质素模型化合物苯基苯乙醚C-O键的加氢裂解

研究了Ni基催化剂上木质素模型化合物苯基苯乙醚中C-O-C键加氢裂解性能.结果表明,Ni/C催化剂显示出优异的加氢裂解能力,苯基苯乙醚的转化率达到99%以上.Ni/C催化剂的还原方法对裂解选择性有重要影响;氢气还原制备的Ni/C-H催化剂上,C-O-C键裂解选择性为85%.Ru/C和Pd/C催化剂上裂解选择性分别为40%和69%.采用碳热还原方法制备的Ni/C-C催化剂,可以实现高选择性加氢和裂解,C-O-C键裂解选择性达到99%以上,其中芳烃化合物收率为44%.这可能与镍组分和载体碳之间的相互作用有关.     

Controlling carbon surface chemistry by alloying: carbon tolerant reforming catalyst

Steam reforming is a process where a hydrocarbon is converted into hydrogen and oxygenated carbon species. Ni is often used as catalyst for the reaction. Long term stability of steam reforming catalysts is governed by their ability to selectively oxidize C atoms while preventing C-C bond formation. In this communication we demonstrate that C atom chemistry over Ni surfaces can be controlled by surface alloying. We show that bimetallic Sn/Ni catalyst is much more carbon-tolerant that monometallic Ni. The main reason for this is that Sn alloying results in dramatically lower rates of C-C bond formation as compared to C-oxidation. The bimetallic catalyst was identified in quantum computational studies of the underlying atomic-scale phenomena that govern C atom surface chemistry. The catalysts were also characterized with various electron- and X-ray-based microscopies and spectroscopies.     

Co-doping a metal (Cr,Mn, Fe,Co, Ni,Cu, and Zn) on Mn/ZSM-5 catalyst and its effect on the catalytic reduction of nitrogen oxides with ammonia

Selective catalytic reduction (SCR) of NO_x by NH₃ over a series of Mn–M/Z catalysts (M = Cr, Mn, Fe, Co, Ni, Cu, Zn, and Z = the ZSM-5 Zeolite) synthesized by wet impregnation method was investigated. Mn–Fe/Z, Mn–Co/Z, and Mn–Cu/Z catalysts exhibited approximately 100 % NO_x conversion over a wide temperature range (200–360 °C) in a defined atmospheric condition, which was noticeably greater than that of Mn–Cr/Z (340–360 °C). Furthermore, the effect of addition of second metal oxide species to the initial Mn/Z catalyst on the structure of catalysts was studied by several characterization techniques. BET measurements revealed high surface area and pore volume of the Mn–Cu/Z catalyst. In addition, the XRD and UV–Vis DR results showed that addition of co-doped metal oxide species improved the dispersion of metal ions and inhibited crystallization of metal oxides. UV–Vis studies also were in good accordance with DTA/TG results confirming the formation of cobalt oxide and copper oxide clusters in Mn–Co/Z and Mn–Cu/Z catalysts, respectively. The FTIR spectra of pyridine adsorption, in addition, suggested the Mn–Cu/Z catalyst contained the most Lewis acid sites leading to more NO_x adsorption capacity.     

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.     

Model reactions for crosslinking polydiacetylene materials

A series of reactions are presented which allowed us to crosslink polydiacetylenes containing carbamate groups in the side chain without attacking the triple bond. These reactions involved syntheses of carbamates and allophanates from butyl alcohol and phenyl isocyanate with metal and tertiary amine catalysts using a model compound, 2,4,7,9-tetramethyl-5-decyn-4,7-diol. Elemental analysis, IR and UV spectroscopy, and high performance liquid chromatography (HPLC) were used as analytical tools. Metal catalysts were found to favor the formation of allophanates in higher yields and purity as compared to tertiary amine catalysts.     

Comparative study of transition metal-doped calcined Malaysian dolomite catalysts for WCO deoxygenation reaction

In the present work, nickel (Ni), zinc (Zn), copper (Cu), cobalt (Co) and iron (Fe) are tested as catalyst dopants on Malaysian dolomite calcined at T = 900 °C (CMD900). The physicochemical properties of all synthesised catalyst are investigated by X-ray diffraction, Brunauer–Emmett–Teller surface area, temperature-programmed desorption of carbon dioxide and scanning emission microscopy. The synthesised catalysts are tested on the basis of the deoxygenation (DO) reaction of waste cooking oil to produce liquid fuels under N₂ atmosphere. The chemical composition of the liquid product is identified by gas chromatography–mass spectroscopy. The overall study suggests that Ni/CMD900 catalyst exhibits the highest performance with over 67.0% conversion and high selectivity (80.2%) with a high proportion of saturated linear hydrocarbons that corresponds to green diesel. Result indicates that Ni/CMD900 is a highly potential DO catalyst with 19.8% oxygenated compound, which is favourable for decarboxylation and/or decarboxylation predominates.     

Cu-Ni-Zn三元脂肪醇胺化催化剂的研究

 长链烷基二甲基叔胺是一类重要的有机中间体,目前其主要的制备工艺是由脂肪醇和二甲胺在脱氢－加氢类催化剂的作用下进行胺化反应．改进脂肪醇胺化催化剂的主要目标是提高其选择性．对以Cu和Ni为活性组分,以碳酸钙为载体的催化剂体系中加入Zn助催化剂组分对催化剂选择性的影响进行了研究．结果发现,在相同Cu／Ni比的条件下,Zn在Cu－Ni催化剂体系中的一个主要作用是能够阻碍氧化态镍的还原,而催化剂的选择性与催化剂中镍的还原程度密切相关．     

Hydrogen production by glycerol reforming in supercritical water over Ni/MgO-ZrO2 catalyst

Nano ZrO₂ and MgO-ZrO₂ were prepared by a self-assembly route and were employed as the support for Ni catalysts used in hydrogen production from glycerol reforming in supercritical water (SCW). The reforming experiments were conducted in a tubular fixed-bed flow reactor over a temperature range of 600–800 °C. The influences of process variables such as temperature, contact time, and water to glycerol ratio on hydrogen yield were investigated and the catalysts were charactered by ICP, BET, XRD and SEM. The results showed that high hydrogen yield was obtained from glycerol by reforming in supercritical water over the Ni/MgO-ZrO₂ catalysts in a short contact time. The MgO in the catalyst showed significant promotion effect for hydrogen production likely due to the formation of the alkaline active site. Even when the glycerol feed concentration was up to 45 wt%, glycerol was completely gasified and transfered to the gas products containing hydrogen, carbon dioxide, and methane along with small amounts of carbon monoxide. At a diluted feed concentration of 5 wt%, near theoretical yield of 7 mole of H₂/mol of glycerol could be obtained.     

Bifunctional Heterogeneous Catalysis of Silica–Alumina‐Supported Tertiary Amines with Controlled Acid–Base Interactions for Efficient 1,4‐Addition Reactions

We report the first tunable bifunctional surface of silica–alumina‐supported tertiary amines (SA–NEt₂) active for catalytic 1,4‐addition reactions of nitroalkanes and thiols to electron‐deficient alkenes. The 1,4‐addition reaction of nitroalkanes to electron‐deficient alkenes is one of the most useful carbon–carbon bond‐forming reactions and applicable toward a wide range of organic syntheses. The reaction between nitroethane and methyl vinyl ketone scarcely proceeded with either SA or homogeneous amines, and a mixture of SA and amines showed very low catalytic activity. In addition, undesirable side reactions occurred in the case of a strong base like sodium ethoxide employed as a catalytic reagent. Only the present SA‐supported amine (SA–NEt₂) catalyst enabled selective formation of a double‐alkylated product without promotions of side reactions such as an intramolecular cyclization reaction. The heterogeneous SA–NEt₂ catalyst was easily recovered from the reaction mixture by simple filtration and reusable with retention of its catalytic activity and selectivity. Furthermore, the SA–NEt₂ catalyst system was applicable to the addition reaction of other nitroalkanes and thiols to various electron‐deficient alkenes. The solid‐state magic‐angle spinning (MAS) NMR spectroscopic analyses, including variable‐contact‐time ¹³C cross‐polarization (CP)/MAS NMR spectroscopy, revealed that acid–base interactions between surface acid sites and immobilized amines can be controlled by pretreatment of SA at different temperatures. The catalytic activities for these addition reactions were strongly affected by the surface acid–base interactions.     

Catalytic steam reforming of model compounds of biomass pyrolysis liquids in fluidized bed reactor with modified Ni/Al catalysts

Catalytic steam reforming of acetic acid and hydroxyacetone (acetol) as model compounds of the aqueous fraction of bio-oil (biomass derived pyrolysis liquids) was studied in fluidized bed reactor over Ni/Al catalysts modified with calcium or magnesium. Attrition tests showed that the use of small quantities of these promoters improved the mechanical strength of the reforming catalyst. An optimum Ca/Al molar ratio of 0.12 and a Mg/Al molar ratio of 0.26 leaded to attrition rates of 0.22 and 0.27 wt%/h, respectively. Steam reforming experiments were performed at 650 °C and a steam to carbon molar ratio (S/C) of 5.58. The promoted catalysts showed different acetic acid steam reforming activities depending on the Ca/Al or Mg/Al molar ratios. Magnesium modified catalysts with a Mg/Al molar ratios of 0.26 and 0.50 showed good performances with almost no activity loss with time in contrast to the calcium modified catalysts that showed higher CO and CH₄ yields. The addition of calcium generated a NiO phase with less interaction with the support. The highest H₂ yield and carbon conversion in acetic steam reforming were obtained by a magnesium promoted catalyst with a Mg/Al ratio of 0.26, while the nonpromoted Ni/Al catalyst showed the best performance in acetol steam reforming. Then, the nature of the organic compound influenced the performance of the different catalysts.     

Controlling the α/γ‐Reactivity of Vinylogous Ketone Enolates in Organocatalytic Enantioselective Michael Reactions

The first regio‐, diastereo‐, and enantioselective direct Michael reaction of β,γ‐unsaturated ketones with nitroolefins is enabled by Brønsted base/hydrogen‐bonding bifunctional catalysis. A squaramide‐substituted tertiary amine catalyzes the reaction of a broad range of β,γ‐unsaturated ketones to proceed at the α‐site exclusively, giving rise to adducts with two consecutive tertiary carbon stereocenters in diastereomeric ratios of up to >20:1 and enantioselectivities generally in the 90–98 % ee range.