Improvement strategies for Ni-based alcohol steam reforming catalysts

Steam reforming(SR)of fossil methane is already a well-known,documented and established expertise in the industrial sector as it accounts for the vast majority of global hydrogen production.From a sustainable development perspective,hydrogen production by SR of biomass-derived feedstock represents a promising alternative that could help to lower the carbon footprint of the traditional process.In this regard,bio-alcohols such as methanol,ethanol or glycerol are among the attractive candidates that could serve as green hydrogen carriers as they decompose at relatively low temperatures in the presence of water compared to methane,allowing for improved H_(2)yields.However,significant challenges remain regarding the activity and stability of nickel-based catalysts,which are most widely used in alcohol SR processes due to their affordability and ability to break C–C,O–H and C–H bonds,yet are prone to rapid deactivation primarily caused by coke deposition and metal particle sintering.In this state-of-the-art review,a portfolio of strategies to improve the performance of Ni-based catalysts used in alcohol SR processes is unfolded with the intent of pinpointing the critical issues in catalyst development.Close examination of the literature reveals that the efforts tackling these recurring issues can be directed at the active metal,either by tuning Ni dispersion and Ni-support interactions or by targeting synergistic effects in bimetallic systems,while others focus on the support,either by modifying acid-base character,oxygen mobility,or by embedding Ni in specific crystallographic structures.This review provides a very useful tool to orient future work in catalyst development.

界面电子扰动促进的C–H键活化

丙烯是重要的化工原料,广泛用于生产聚丙烯、环氧丙烷、丙烯醛、丙烯腈和丙酮等重要化工中间体以及合成树脂、合成橡胶和许多精细化工产品.目前生产丙烯的方法主要有石脑油裂解、催化流化裂化、丙烷脱氢、烯烃复分解和甲醇制烯烃等.其中丙烷脱氢因具有较高的丙烯选择性和较低的原料成本而备受关注,尤其是页岩气在全球的大量发现和开采,使得丙烷的原料成本持续下降,丙烷脱氢技术的迅速发展,但高效催化剂研发成为提升生产效率的关键.商业Pt基催化剂通常采用合金化的手段优化Pt颗粒的表面结构和中间体的吸附状态,进而获得较好的催化性能,但金属助剂的引入在一定程度上会弱化Pt位点的C–H键活化能力.针对该问题,本文从惰性C–H键活化角度出发,揭示了一种新的C–H键界面活化机制.通过金属-载体强相互作用诱导形成Pt-Ga_(2)O_(3)反向界面结构,密度泛函理论计算结果表明,Pt与Ga_(2)O_(3)之间存在强烈的电子扰动现象,使得界面处O位点表现出类金属的电子特性,在费米能级附近存在连续的电子态,这与Ga_(2)O_(3)本身离散性电子态呈明显对比,显示出Pt-Ga_(2)O_(3)反向界面结构的独特性质,使得界面O位点表现出极强的H吸附能和C–H键活化能力,其催化丙烷分子中亚甲基C–H键断裂的活化能仅为0.21 eV,远低于Pt(111)晶面的0.64 eV.原位红外光谱结果表明,反应过程中该界面结构会产生大量的羟基.根据过渡态的精细结构可知,反应位点是通过抓取H原子并随即稳定产生的C自由基完成C–H键的断裂,分析结果表明,H吸附能与反应能垒有着紧密的关联,而Pt-Ga_(2)O_(3)反向界面结构中,Pt基底赋予界面O位点独特的电子结构,同时也可以作为电子受体接收H传递的电子,从而表现出极强的H结合能和C–H键活化能力,其C–H断裂能垒要远低于各类Pt位点.进一步的分析表明,首个C–H键在Pt–O界面位发生断裂后,所形成的H物种会由O位点溢流至Pt颗粒表面,最终以H_(2)形式释放,留下的2-丙基碎片再经历甲基的C–H键断裂、H溢流、脱氢等步骤形成丙烯分子.而Pt颗粒表面的Ga_(2)O_(3)团簇也起到分割表面位点的作用,促进丙烯脱附的同时,有效弱化C–C键的断裂趋势,减少裂解副产物,生成丙烯的选择性超过99%.综上所述,本文构建的Pt/Ga-Al_(2)O_(3)界面位催化剂在丙烷脱氢反应中的性能要明显优于Pt/Al_(2)O_(3)以及工业常用的PtSn/Al_(2)O_(3)催化剂,揭示了一种全新的C–H键活化策略,并探究其中的化学机制,既可以深化对界面协同催化的理解,又可以为高性能催化剂的设计提供借鉴和指导.

Promotional effects of Ru and Fe on Ni/ZrO_(2) catalyst during CO_(2) methanation:A comparative evaluation of the mechanism

Ni-based catalysts are widely investigated non-noble metal-based systems for CO_(2)methanation.However,their industrial application is still limited due to lower activity at low-temperature and catalyst deactivation.Incorporating a second metal such as Ru and Fe is considered as a successful strategy to overcome these challenges through alloy formation or the synergies provided by the interplay of two adjacent metallic sites.Nonetheless,their promotional effect on the CO_(2)methanation mechanism under similar conditions has not been reported yet.In this work,Fe and Ru-promoted Ni/ZrO_(2)catalysts were investigated to evaluate their promotional effect on the mechanism.The Ni/Fe ratio was first optimized and a CO_(2)conversion rate of 37.7 mmolCO_(2)/(molNi+Fes)and 96.3%CH^(4)selectivity was obtained over the Ni_(0.8)Fe_(0.2)/ZrO_(2)catalyst.In comparison with Ni_(0.8)Fe_(0.2)/ZrO_(2),Ni_(0.8)Ru_(0.2)/ZrO_(2)prepared with the same composition showed higher activity and stability in CO_(2)methanation.Characterization results indicate alloys formation and H spillover for Ni_(0.8)Ru_(0.2)/ZrO_(2)to be responsible for promotion.Besides,in situ DRIFTS studies evidenced the occurrence of both CO_(2)dissociative and associative pathways over Ni_(0.8)Ru_(0.2)/ZrO_(2)catalyst,while solely the CO_(2)associative pathway occurred for Ni_(0.8)Fe_(0.2)/ZrO_(2)

H覆盖对费托合成催化剂CO活化影响的理论计算研究

Fe基和Co基催化剂是最理想的费托合成催化剂,随着计算机模拟技术在催化领域快速地发展,深入理解Fe基和Co基催化剂表面的微观反应机理成为可能。采用理论计算方法,研究了不同H覆盖度的Fe基(反应条件:温度320℃、压力1 MPa以及n(H_(2)):n(CO)=1:1)、Co基(反应条件:温度240℃、压力1 MPa以及n(H_(2)):n(CO)=2:1)费托合成催化剂的表面结构以及H覆盖对CO活化与解离的影响。通过氢气化学势与氢吸附吉布斯自由能的线性关系确定了Fe基、Co基费托合成催化剂热力学最优的H覆盖表面模型,分别为H覆盖度为11/42的χ-Fe_(5)C_(2)(510)表面和H覆盖度为24/36的HCPCo(0001)表面。研究了洁净的催化剂表面与H覆盖的催化剂表面的CO解离机理及相关反应能垒,发现H覆盖会改变CO解离路径且增大CO解离能垒,相较于洁净的χ-Fe_(5)C_(2)(510)和HCPCo(0001)表面,H覆盖的χ-Fe_(5)C_(2)(510)和HCPCo(0001)表面的CO解离能垒分别升高了5.4%和20.3%。通过对表面态密度以及晶体轨道哈密顿布居的计算解释了H覆盖影响CO活化与解离的本质原因。

XY-H催化剂在淤浆法HDPE装置上的应用

介绍了XY$CH型催化剂在兰州石化公司7万t/a淤浆法高密度聚乙烯装置上的试用情况,并与日本三井油化公司PZ催化剂进行了比较。结果表明,XY$CH催化剂活性较高,氢调敏感,可生产出各项性能均能达到国标优级品标准且拉伸强度和扯断伸长率均优于PZ催化剂的5000S产品。

基于PDFF的直线电机驱动XY平台H_∞交叉耦合控制

XY平台直线伺服系统中,负载扰动、机械惯性及双轴响应速度不匹配会影响轮廓加工精度,为此提出了一种将PDFF及H∞交叉耦合控制相结合的控制策略。单轴速度控制器采用兼顾快速性和鲁棒性的PDFF控制,间接减小轮廓误差。并在X、Y轴间引入交叉耦合控制,将基于PDFF的XY平台交叉耦合控制框架等效为一反馈系统,采用H∞次优方法设计交叉耦合控制器,直接减小轮廓误差。仿真结果表明该控制方案可增强系统的鲁棒性,提高系统的快速性和轮廓加工精度。

基于H_∞反馈的直接驱动XY平台切向轮廓控制设计

为了提高XY平台的轮廓加工精度,在分析系统轮廓误差的基础上,提出将H∞速度反馈控制器和切向-轮廓控制器(TCC)相结合的控制策略。在速度环内采用H∞鲁棒控制理论设计反馈控制器,在具有模型摄动及外部干扰的情况下,保证了闭环系统的鲁棒稳定性和鲁棒性能,TCC使得XY平台之间的耦合作用消除,且轮廓控制器设计变得更加直接和简单。单轴系统采用IP(积分-比例)控制与速度前馈控制相结合的复合控制器。仿真结果表明所设计控制系统在保证具有较好的跟踪性能、鲁棒性能的同时轮廓精度大大提高。

Synergistic degradation of phenols by bimetallic CuO-Co_3O_4@γ-Al_2O_3 catalyst in H_2O_2/HCO_3^- system

The development of new catalytic techniques for wastewater treatment has long attracted much attention from industrial and academic communities.However,because of catalyst leaching during degradation,catalysts can be short lived,and therefore expensive,and unsuitable for use in wastewater treatment.In this work,we developed a bimetallic CuO-Co3O4@γ-Al2O3 catalyst for phenol degradation with bicarbonate-activated H2O2.The weakly basic environment provided by the bicarbonate buffer greatly suppresses leaching of active Cu and Co metal ions from the catalyst.X-ray diffraction and X-ray photoelectron spectroscopy results showed interactions between Cu and Co ions in the CuO-Co3O4@γ-Al2O3 catalyst,and these improve the catalytic activity in phenol degradation.Mechanistic studies using different radical scavengers showed that superoxide and hydroxyl radicals both played significant roles in phenol degradation,whereas singlet oxygen was less important.

H_2-induced CO adsorption and dissociation over Co/Al_2O_3 catalyst

The activation of adsorbed CO is an important step in CO hydrogenation. The results from TPSR of pre-adsorbed CO with H2 and syngas suggested that the presence of H2 increased the amount of CO adsorption and accelerated CO dissociation. The H2 was adsorbed first, and activated to form H＊ over metal sites, then reacted with carbonaceous species. The oxygen species for CO2 formation in the presence of hydrogen was mostly OH^＊, which reacted with adsorbed CO subsequently via CO^＊＋OH^＊ → CO2^＊＋H^＊; however, the direct CO dissociation was not excluded in CO hydrogenation. The dissociation of C-O bond in the presence of H2 proceeded by a concerted mechanism, which assisted the Boudourd reaction of adsorbed CO on the surface via CO^＊＋2H^＊ → CH^＊＋OH^＊. The formation of the surface species （CH） from adsorbed CO proceeded as indicated with the participation of surface hydrogen, was favored in the initial step of the Fischer-Tropsch synthesis.

Preferential oxidation of CO in excess H_2 over the CeO_2/CuO catalyst: Effect of initial support

Three series of CeO2/CuO samples were prepared by impregnation method and characterized by XRD, N2 adsorption-desorption, temperatureprogrammed reduction （TPR）, XPS and TEM techniques. In comparison with the samples prepared with CuO as initial support, the samples with Cu（OH）2 as initial support have higher reducibilities and smaller relative TPR peak areas, and also larger specific surface areas at calcina- tion temperatures of 400 ℃--600 ℃. As a result, Cu（OH）2 is better than CuO as initial support for preferential oxidation of CO in excess H2 （CO-PROX）. The best catalytic performance was achieved on the sample calcined at 600 ℃ and with an atomic ratio of Ce/Cu at 40%. XPS analyses indicate that more interface linkages Ce-O-Cu could be formed when it was calcined at 600 ℃. And the atomic ratio of Ce/Cu at 40% led to a proper reducibility for the sample as illustrated by the TPR measurements.

Evaluation of H2 Influence on the Evolution Mechanism of NOx Storage and Reduction over Pt–Ba–Ce/c-Al2O3 Catalysts

In this investigation, Pt–Ba–Ce/c-Al2O3 catalysts were prepared by incipient wetness impregnation and experiments were performed to evaluate the influence of H2 on the evolution mechanism of nitrogen oxides (NOx) storage and reduction (NSR). The physical and chemical properties of the Pt–Ba–Ce/c- Al2O3 catalysts were studied using a combination of characterization techniques, which showed that PtOx, CeO2, and BaCO3, whose peaks were observed in X-ray diffraction (XRD) spectra, dispersed well on the c-Al2O3, as shown by transmission electron microscope (TEM), and that the difference between Ce3+ and Ce4+, as detected by X-ray photoelectron spectroscopy (XPS), facilitated the migration of active oxygen over the catalyst. In the process of a complete NSR experiment, the NOx storage capability was greatly enhanced in the temperature range of 250–350℃, and reached a maximum value of 315.3μmol·gcat^-1 at 350℃, which was ascribed to the increase in NO2 yield. In a lean and rich cycling experiment, the results showed that NOx storage efficiency and conversion were increased when the time of H2 exposure (i.e., 30, 45, and 60 s) was extended. The maximum NOx conversion of the catalyst reached 83.5% when the duration of the lean and rich phases was 240 and 60 s, respectively. The results revealed that increasing the content of H2 by an appropriate amount was favorable to the NSR mechanism due to increased decomposition of nitrate or nitrite, and the refreshing of trapping sites for the next cycle of NSR.

Renewable hydrogen production from steam reforming of glycerol(SRG)over ceria-modified Y-alumina supported Ni catalyst

Excess crude glycerol derived as a by-product from biodiesel industry prompts the need to valorise glycerol to value-added chemicals.In this context,catalytic steam reforming of glycerol(SRG) was proposed as a promising and sustainable alternative for producing renewable hydrogen(H2).Herein,the development of nickel(Ni) supported on ceria-modified mesoporous γ-alumina(γ-Al2 O3) catalysts and their applications in catalytic SRG(at550-750℃ atmospheric pressure and weight hourly space velocity,WHSV,of 44,122 ml·g^-1·h^-1(STP)) is presented.Properties of the developed catalysts were characterised using many technique s.The findings show that ceria modification improved Ni dispersion on γ-Al2 O3 catalyst support with highly active small Ni particles,which led to a remarkable catalytic performance with the total glycerol conversion(ca.99%),glycerol conversion into gaseous products(ca.77%) and H2 yield(ca.62%).The formation rate for H2 production(14.4 ×10^(-5)mol·s^-1·g^-1, TOF(H2)=3412 s^-1) was significantly improved with the Ni@12 Ce-Al2 O3 catalyst,representing nearly a 2-fold increase compared with that of the conventional Ni@AI2 O3 catalyst.In addition,the developed catalyst also exhibited comparatively high stability(for 12 h) and coke resistance ability.

Effects of support pore size on new Cs_(2.5)H_(0.5)PW_(12)O_(40)/SiO_2 catalysts for the ring-opening polymerization of tetrahydrofuran

Mesoporous silica supported Cs2.5H0.5PW12O40 catalysts were prepared by impregnation method, and several silica supports with different pore size were utilized. N2 adsorption, XRD and ICP-AES techniques were utilized to characterize the silica supports and catalysts. XRD results showed that the dispersion of Cs2.5H0.5PW12 was better for the silica support with larger pore size. The catalytic activity results showed that the pore size played important role on the catalyst activity and the molecular weight of PTHF. When Cs2.5H0.5PW12O40 was dispersed on larger pore size silica support, the catalysts showed good performances for the synthesis of PTHE The molecular weight of PTHF product on the sample in which Cs2.5H0.5PW12O40 was dispersed on larger pore support was higher than that on the catalyst with smaller pore support. The leaching amounts of the active components for the supported Cs2.5H0.5PW12O40 catalysts were much lower. After five reaction cycles, there were still good activities and stabilities for the supported Cs2.5H0.5PW12O40 catalysts with larger pore silica supports. These results were much better than those of the supported heteropolyacid H3PW12O40 catalyst.

Preparation of p-1,1,3,3-Tetramethylbutylphenol by Using Nafion-H Catalyst

p-1, 1, 3, 3-Tetramethylbutylphenol was prepared by the alkylation of the phenol with Nafion catalyst in extremely high yield. Various reaction conditions were investigated, including the reaction temperature, reaction time, ratio of the starting material, amount of the Nafion catalyst and the recycle times of the catalyst.

Oxidative Desulfurization of DBT with H2O2 over 3DOM H3PW12O40/Al2O3 Catalyst

A series of heteropoly acid (HPA) based Al2O3 catalysts with three-dimensional ordered (3DOM) structure were synthesized by colloidal crystal template method.Interconnected macropores (250 nm) could be clearly observed by scanning electron microscope (SEM) and transmission electron microscope (TEM).Mesopores could be detected by N2 adsorption-desorption isotherms which further confirmed the 3DOM structural characteristics of catalyst.Moreover,Keggin-type HPW was highly dispersed in the Al2O3 framework,which suggested by powder X-ray diffraction (XRD) and Fourier transform infrared spectra (FT-IR) results.The oxidation desulfurization (ODS) performance of 3DOM H3PW12O40/Al2O3 of refractory sulphur compounds was evaluated in the presence of hydrogen peroxide.It oxidized 98.5% of dibenzothiophene (DBT) into corresponding sulfone within 3 h,which exhibited superior ODS performance than corresponding mesoporous and microporous H3PW12O40/Al2O3 catalyst.The enhancement of ODS efficiency is related to the improvement of mass transfer of DBT in the pore channel resulting from the interconnected 3DOM structure.Furthermore,the as-prepared catalyst still demonstrates outstanding cycle performance after 6 runs,which could be easily recovered from the model fuel.

Effect of CO_2 on the structural variation of Na_2WO_4/Mn/SiO_2 catalyst for oxidative coupling of methane to ethylene

In this work,the influence of CO2 on the structural variation and catalytic performance of Na2WO4/Mn/Si O2 for oxidative coupling of methane to ethylene was investigated. The catalyst was prepared by impregnation method and characterized by XRD,Raman and XPS techniques. Appropriate amount of CO2 in the reactant gases enhanced the formation of surface tetrahedral Na2WO4 species and promoted the migration of O in MOx,Na,W from the catalyst bulk to surface,which were favorable for oxidative coupling of methane. When the molar ratio of CH4/O2/CO2 was 3/1/2,enriched surface tetrahedral Na2WO4 species and high surface concentration of O in MOx,Na,W were detected,and then high CH4 conversion of 33.1% and high C2H4 selectivity of 56.2% were obtained. With further increase of CO2 in the reagent gases,the content of active surface tetrahedral Na2WO4 species and surface concentration of O in MOx,Na,W decreased,while that of inactive species（Mn WO4 and Mn2O3） increased dramatically,leading to low CH4 conversion and low C2H4 selectivity. It could be speculated that Na2WO4 crystal was transformed into Mn WO4 crystal with excessive CO2 added under the reaction conditions. Pretreatment of Na2WO4/Mn/Si O2 catalyst by moderate amount of CO2 before OCM also promoted the formation of Na2WO4 species.

Synthesis, Structure and Catalytic Activity of a Manganese(Ⅲ) Complex Based on 2-(2-Hydroxyphenyl)-5,6-dichlorobenzimidazole Ligands

A new ligand, 2-（2-hydroxyphenyl）-5,6-dichlorobenzimidazole, H2pbmCl2（1）, and a novel MnIII complex, [MnIII（HpbmCl2）（pbmCl2）（DMF）2]（2）,（DMF = N,N-dimethylformamide）, have been synthesized and characterized. The crystal of compound 1（C13H8Cl2N2O, Mr = 279.12） belongs to the monoclinic system, space group P21 with a = 3.770（5）, b = 25.20（3）, c = 5.865（7） A, = 92.727（17）o, V = 556.6（12） A3, Z = 2, Dc = 1.665 g/cm^3, S = 1.137, μ= 0.568 mm^-1, F（000） = 284, the final R = 0.0876 and wR = 0.2334 for 1848 independent reflections. The molecule is planar due to the presence of a strong intramolecular hydrogen bond between O–H group of phenol and N atom of imidazole. H2pbmCl2（1） molecules are arranged into a one-dimensional linear chain through intermolecular hydrogen bonds（N–H…O and C–H…Cl）. The crystal of complex 2（C32H27Cl4MnN6O4, Mr = 756.34） belongs to the monoclinic system, space group P21/c with a = 19.043（10）, b = 10.808（5）, c = 18.704（11）A, β= 115.540（6）°, V = 3473（3） A3, Z = 4, Dc = 1.446 g/cm^3, S = 1.3, μ = 0.733 mm-1, F（000） = 1544, the final R = 0.1219 and wR = 0.2681 for 7811 independent reflections. The Mn ion adopts a distorted octahedral geometry coordinated by two deprotonated H2pbmCl2 ligands and two DMF molecules. The [MnIII（HpbmCl2）（pbmCl2）（DMF）2] molecules are arranged into a three-dimensional structure through hydrogen bonds（N–H…N, C–H…N and C–H…Cl） and weak π···πinteractions. The activity measurements suggest that complex 2 is able to serve as a catalyst for H2O2 disproportionation reaction to form O2 in neutral water solution.

Investigation of water adsorption and dissociation on Au_1/CeO_2 single-atom catalysts using density functional theory

We examined the water adsorption and dissociation on ceria surfaces as well as ceria‐supported Au single‐atom catalysts using density functional theory calculations.Molecular and dissociative water were observed to coexist on clean CeO2and reduced Au1/CeO2?x surfaces because of the small difference in adsorption energies,whereas the presence of dissociative water was highly favorable on reduced CeO2?x and clean Au1/CeO2surfaces.Positively charged Au single atoms on the ceria surface not only provided activation sites for water adsorption but also facilitated water dissociation by weakening the intramolecular O-H bonds.In contrast,negatively charged Au single atoms were not reactive for water adsorption because of the saturation of Au5d and6s electron shells.This work provides a fundamental understanding of the interaction between water and single‐atom Au catalysts.

Improved Performance of W/HZSM-5 Catalysts for Dehydroaromatization of Methane

The dehydroaramatization of methane over W-supported ZSM-5 with varying degrees of Li+ ion-exchanged catalysts was studied with and without oxygen at 1073 K and atmospheric pressure. Catalyst activity and stability were found to be influenced by the catalyst acidity related to Bronsted acid sites and by the presence of oxygen in the feed. The NH3-TPD and FTIR-pyridine results demonstrated that partially exchanged of H+ ions by Li+ into the W/HZSM-5 catalysts could be used to control the amount of strong acid sites on the catalyst surface. Without oxygen, the 3WHLi-Z (5:1) catalyst that has strong acid sites equal to nearly 74% of the original strong acid sites in the parent HZSM-5 exhibited the highest methane conversion and selectivity towards aromatics. However, the catalyst deactivated in a five hour period. In the presence of oxygen, the catalyst activity and stability could be improved further. The results of this study revealed that a suitable amount of strong Bronsted acid sites as well as oxygen addition in the feed increased the catalyst activity and stability. The 3WHLi-Z(5:1) catalyst exhibited improved performance in the dehydroaromatization of methane.