焙烧温度对Cu-Ce/MgO催化合成气制低碳醇性能的影响

采用并流共沉淀法在不同焙烧温度下制备Cu-Ce/Mg O催化剂,考察焙烧温度对其催化CO加氢合成低碳混合醇反应性能的影响,并借助X射线衍射(XRD)、N2物理吸附(N2-adsorption)等手段对催化剂的结构进行表征。结果表明,随着焙烧温度的升高,催化剂中Ce O2晶粒增大,催化剂比表面积减小;在CO加氢反应中,焙烧温度的适当升高明显增加了催化剂活性组元之间的相互作用,使催化剂活性及低碳醇选择性明显升高;450℃的焙烧温度下,CO的转化率为54.51%,醇的选择性达到38.40%。

Ce添加量对Cu-Ce/MgO催化合成气制低碳醇性能的影响

采用共浸渍法制备不同Ce含量(相对于MgO的摩尔分数为0~15%)的Cu-Ce/MgO催化剂,采用X射线衍射(XRD)、N_2物理吸附(N_2-adsorption)等手段对催化剂的结构进行表征,并在连续流动微型固定床反应器中考察其催化CO加氢合成低碳混合醇的反应性能.结果表明,不同含量的Ce助剂的添加对催化剂的物理结构、表面物相以及醇的选择性和产物分布都产生一定的影响.当Ce的负载量为10%时,催化剂样品的比表面积达到最大(64.23m2·g^(-1)),CO的转化率较高(42.3%),醇的选择性最高(43.7%),CHx的选择性最低,催化剂的活性最高.

Effect of Ni loadings on the activity and coke formation of MgO-modified Ni/Al_2O_3 nanocatalyst in dry reforming of methane

MgO-modified Ni/Al2O3 catalysts with different Ni loadings were prepared and employed in dry reforming of methane （DRM）. The effect of Ni loadings on the activity and coke formation of Ni/MgO-A1203 catalysts were investigated. The synthesized catalysts were characterized by XRD, N2 adsorption-desorption, SEM, TPO and TPR techniques. The obtained results showed that increasing nickel loading decreased the BET surface area and increased the catalytic activity and amount of deposited carbon. In addition, the effect of gas hourly space velocity （GHSV） and feed ratio were studied.

Screening of MgO- and CeO_2-Based Catalysts for Carbon Dioxide Oxidative Coupling of Methane to C_(2+) Hydrocarbons

The catalyst screening tests for carbon dioxide oxidative coupling of methane (CO2-OCM) have been investigated over ternary and binary metal oxide catalysts. The catalysts are prepared by doping MgO- and CeO2-based solids with oxides from alkali (Li2O), alkaline earth (CaO), and transition metal groups (WO3 or MnO). The presence of the peroxide (O2-2) active sites on the Li2O2, revealed by Raman spectroscopy, may be the key factor in the enhanced performance of some of the Li2O/MgO catalysts. The high reducibility of the CeO2 catalyst, an important factor in the CO2-OCM catalyst activity, may be enhanced by the presence of manganese oxide species. The manganese oxide species increases oxygen mobility and oxygen vacancies in the CeO2 catalyst. Raman and Fourier Transform Infra Red (FT-IR) spectroscopies revealed the presence of lattice vibrations of metal-oxygen bondings and active sites in which the peaks corresponding to the bulk crystalline structures of Li2O, CaO, WO3 and MnO are detected. The performance of 5%MnO/15%CaO/CeO2 catalyst is the most potential among the CeO2-based catalysts, although lower than the 2%Li2O/MgO catalyst. The 2%Li2O/MgO catalyst showed the most promising C2+ hydrocarbons selectivity and yield at 98.0% and 5.7%, respectively.

Effect of MgO promoter on Ni-based SBA-15 catalysts for combined steam and carbon dioxide reforming of methane

A series of Ni/SBA-15 catalysts with Ni contents ranging from 5 wt% to 15 wt%, as well as another series of 10%Ni/MgO/SBA-15 catalysts, in which the range of the MgO content was from 1 wt% to 7 wt%, were prepared, and their catalytic performances for the reaction of combined steam and carbon dioxide reforming of methane were investigated in a continuous flow microreactor. The structures of the catalysts were characterized using the XRD, H2-TPR and CO2-TPD techniques. The results indicated that the CO selectivity for this reaction was very close to 100%, and the H2/CO ratio of the product gas could be controlled by changing the H2O/CO2 molar ratio of the feed gas. The simultaneous and plentiful existing of steam and CO2 had a significant influence on the catalytic performance of the 10%Ni/SBA-15 catalyst without modification. After reacting at 850 °C for 120 h over this catalyst, the CH4 conversion dropped from 98% to 85%, and the CO2 conversion decreased from 86% to 53%. However, the 10%Ni/3%MgO/SBA-15 catalyst exhibited a much better catalytic performance, and after reacting for 620 h, the CO2 conversion over this catalyst dropped from 92% to around 77%, while the CH4 conversion was not decreased. Oxidation of the Ni0 species as well as carbon deposition during the reaction were the main reasons for the deactivation of the catalyst without modification. On the other hand, modification by the MgO promoter improved the dispersion of the Ni0 species, and enhanced the CO2 adsorption affinity which in turn depressed the occurring of carbon deposition, and thus retarded the deactivation process.

Ni/MgO catalyst prepared using atmospheric high-frequency discharge plasma for CO_2 reforming of methane

A new type of Ni/MgO catalyst was prepared using atmospheric high-frequency discharge cold plasma. The influences of conventional method, plasma method, and plasma plus calcination method on the catalytic activity were studied and the CO2 reforming of methane was chosen as the probe reaction. The catalysts were characterized by X-ray diffraction （XRD）, transmission electron microscope （TEM）, X-ray photoelectron spectroscopy, and CO2 temperature-programmed surface reaction techniques. The results suggested that the nickel-based catalyst prepared by plasma plus calcination method possessed a smaller particle size and a higher dispersion of active component, better low-temperature activity and enhanced anti-coking ability. The conversion of CO2 and CH4 was 90.70% and 89.37%, respectively, and the reaction lasted for 36 h without obvious deactivation under 101.325 kPa and 750°C with CO2/CH4 = 1/1.

Hydrogen production by glycerol reforming in supercritical water over Ni/MgO-ZrO_2 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 ℃. 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.

Influence of MgO contents on silica supported nano-size gold catalyst for carbon monoxide total oxidation

A series of nano-size gold catalysts were prepared by deposition-precipitation method using silica material promoted with different amounts of MgO as the carrier. The influences of MgO addition on the structure and property of the nano-size gold catalysts were characterized by X-ray diffraction （XRD）, transmission electron microscopy （TEM）, O2 temperature-programmed desorption （O2-TPD）, and inductively coupled with plasma atomic emission spectroscopy （ICP-AES） techniques. The total oxidation of CO was chosen as the probe reaction. The results suggest that for the gold catalysts supported on the silica material after MgO modification, the size of the gold particles is pronouncedly reduced, the oxygen mobility is enhanced, and the catalytic activity for low-temperature CO oxidation is greatly improved. The gold catalyst modified by 6 wt% MgO （Mg/SiO2 weight ratio） shows higher CO oxidation activity, over which the temperature of CO total oxidation is lower about 150 K than that over the silica directly supported gold catalyst.

Catalytic activity of Cu/ZnO catalysts mediated by MgO promoter in hydrogenation of methyl acetate to ethanol

Hydrogenation of methyl acetate is a key step in ethanol synthesis from dimethyl ether carbonylation and Cu-based catalysts are widely studied.We report here that the hydrogenation activity of Cu/ZnO catalysts can be enhanced by the addition of MgO promoter.The evolution of crystal phases during coprecipitation and the physicochemical properties of calcined and reduced catalysts by X-ray diffraction(XRD),thermogravimetric(TG)-mass spectrometry(MS),Brunauer-Emmett-Teller(BET),transmission electron microscopy(TEM),N_(2)O titration,in situ CO-Fourier transform infrared spectroscopy(FTIR)and H_(2)-temperature programmed reduction(H_(2)-TPR)reveal that the promoter effect likely lies in the presence of Mg^(2+).A proper amount of Mg^(2+)mediates the precipitation process of Cu and Zn,leading to preferable formation of aurichalcite(Cu_(x)Zn_(1-x))5(CO_(3))_(2)(OH)_(6) crystal phase and a small amount of basic carbonates such as hydrozincite Zn_(5)(CO_(3))_(2)(OH)_(6) and malachite Cu_(2) CO_(3)(OH)_(2).The presence of aurichalcite strengthens the interaction between Cu and Zn species,and thus enhances the dispersity of CuO species and helps generation of Cu^(+)species on reduced catalysts.Furthermore,the performance of Cu/ZnO catalysts exhibits an optimal dependence on the Mg loading,i.e.,17.5%.However,too much Mg^(2+)in the precipitation liquid prohibits formation of aurichalcite but enhances formation of basic nitrates,leading to a dramatically reduced hydrogenation activity.These findings may find applications for optimization of other Cu-based catalysts in a wider range of hydrogenation reactions.

Insight into MgO promoter with low concentration for the carbon-deposition resistance of Ni-based catalysts in the CO_2 reforming of CH_4

The CO2reforming of CH4is studied over MgO‐promoted Ni catalysts,which were supported on alumina prepared from hydrotalcite.This presents an improved stability compared with non‐promoted catalysts.The introduction of the MgO promoter was achieved through the‘‘memory effect’’of the Ni‐Al hydrotalcite structure,and ICP‐MS confirmed that only0.42wt.%of Mg2+ions were added into the Ni‐Mg/Al catalyst.Although no differences in the Ni particle size and basicity strength were observed,the Ni‐Mg/Al catalyst showed a higher catalytic stability than the Ni/Al catalyst.A series of surface reaction experiments were used and showed that the addition of a MgO promoter with low concentration can promote CO2dissociation to form active surface oxygen arising from the formation of the Ni‐MgO interface sites.Therefore,the carbon‐resistance promotion by nature was suggested to contribute to an oxidative environment around Ni particles,which would increase the conversion of carbon residues from CH4cracking to yield CO on the Ni metal surface.?2018,Dalian Institute of Chemical Physics,Chinese Academy of Sciences.Published by Elsevier B.V.All rights reserved.

CH_4-CO_2 reforming to syngas over Pt-CeO_2-ZrO_2/MgO catalysts: Modification of support using ion exchange resin method

Pt-CeO2-ZrO2/MgO （Pt-CZ/MgO） catalysts with 0.8 wt% Pt, 3.0 wt% CeO2 and 3.0 wt% ZrO2 were prepared by wet impregnation method. Support MgO was obtained using ion exchange resin method or using commercial MgO. XRD, BET, SEM, TEM, DTA-TG and CO2-TPD were used to characterize the catalysts. CH4-CO2 reforming to synthesis gas （syngas） was performed to test the catalytic behavior of the catalysts. The catalyst Pt-CZ/MgO-IE（D） prepared using ion exchange resin exhibits more regular structure, smaller and more unique particle sizes, and stronger basicity than the catalyst Pt-CZ/MgO prepared from commercial MgO. At 1073 K and atmospheric pressure, Pt-CZ/MgO-IE（D） catalyst has a higher activity and greater stability than Pt-CZ/MgO catalyst for CH4-CO2 reforming reaction at high gas hourly space velocity of 36000 mL/（g.h） with a stoichiometric feed of CH4 and C02. Activity measurement and characterization results demonstrate that modification of the support using ion exchange resin method can promote the surface structural property and stability, therefore enhancing the activity and stability for CH4-CO2 reforming reaction.

Effect of the Ni size on CH4/CO2 reforming over Ni/MgO catalyst：A DFT study

Carbon deposition is sensitive to the metal particle sizes of supported Ni catalysts in CH_4/CO_2 reforming.To explore the reason of this phenomenon,Ni4,Ni8,and Ni12 which re flect the different cluster thicknesses supported on the MgO(100) slabs,have been employed to simulate Ni/MgO catalysts,and the reaction pathways of CH_4/CO_2 reforming on Nix/MgO(100) models are investigated by density functional theory.The reforming mechanisms of CH_4/CO_2 on different Nix/MgO(100) indicate the energy barriers of CH_4 dissociated adsorption,CH dissociation,and C oxidation three factors are all declining with the decrease of the Ni cluster sizes.The Hirshfeld charges analyses of three steps as described above show only Ni atoms in bottom two layers can obtain electrons from the MgO supporters,and the main electron transfer occurs between adsorbed species and their directly contacted Ni atoms.Due to more electron-rich Ni atoms in contact with the MgO supporters,the Ni/MgO catalysts with small Ni particles have a strong metal particle size effect and lead to its better catalytic activity.

Reduction of Sulphur-containing Aromatic Nitro Compounds with Hydrazine Hydrate over Iron(III) Oxide-MgO Catalyst

Sulphur-containing aromatic amines were prepared efficiently in good to excellent yields by reduction of the corresponding sulphur-containing aromatic nitro compounds with hydrazine hydrate in the presence of iron（Ⅲ） oxide-MgO catalyst. The catalyst exhibited high activity and stability for the reduction of sulphur-containing aromatic nitro compounds. The yields of sulphur-containing aromatic amines were up to 91-99 % at 355 K after reduction for 1-4 h over this catalyst.

An Ab Initio Study of N_2O Decomposition on MgO Catalyst

Ab initio calculations based on density functional theory have been used to study thedecompsition of N_2O on MgO. The reaction is predicted to occur on O_3c and O_(4c) atoms, but not onO_(5c) atoms, with an activation barrier of 25-27 kcal/mol, in agreement with the experimental valueof 35 kcal/mol. Natural bond orbital analysis shows that the reaction leaves O ad-atoms on thosesurface O anions to form a peroxide-like 'O^2_(2-)' species. The )O-O bond stretching frequency ispredicted to be in the range from 820 cm(-1) to 825 cm(-1).

THE PREPARATION CHEMISTRY OF V/MgO CATALYST FOR OXIDATIVE DEHYDROGENATION OF ETHYLBENZENE

The structures and catalytic performances of V_2O_5, Mg_3V_2O_8 and V/MgO catalysts have been correlated by means of XRD, FTIR, TPR and flow micro-reactor tests. The postulation about active site has been made. Based on it, better catalysts have been first prepared via grafting and modification with Sb which are better than that via impregnation.

Advanced heterolytic H_(2) adsorption of K-added Ru/MgO catalysts for accelerating hydrogen storage into aromatic benzyltoluenes

Herein,we report a highly active K-added Ru/MgO catalyst for hydrogen storage into aromatic benzyltoluenes at low temperatures to advance liquid organic hydrogen carrier technology.The hydrogenation activity of Ru/K/MgO catalysts exhibits a volcano-shaped dependence on the K content at the maximum with 0.02 wt%.This is in good agreement with the strength and capacity of H_(2) adsorption derived from basicity,despite a gradual decrease in the textural property and the corresponding increase in the Ru particle size with increasing the K content.Density functional theory calculations show that heterolytic hydrogen adsorption properties(strength and polarization)are facilitated up to a specific density of K on the Ru–MgO interface and excessive K suppresses heterolytic H_(2) adsorption by direct interaction between K and hydrogen,assuring the hydrogenation activity and H_(2) adsorption capability of Ru/K/MgO catalysts.Hence,the Ru/K/MgO catalyst,when K is added in an optimal amount,is highly effective to accelerate hydrogen storage kinetics at low temperatures owing to the enhanced heterolytic H_(2) adsorption.

CATALYTIC PERFORMANCE OF ETHYLENE HYDROFORMYLATION OVER[H_XRu_3(CO)_9(CCO)]^(2-X)/SiO_2-Al_2O_3,SiO_2 AND MgO(X=0-2)CATALYSTS

The various surface species[H_XRu_3(CO)_9(CCO)]^(2-X)(X=0-2)prepared from impregnation of[PPN]_2[Ru_3(CO)_9(CCO)]on SiO_2-Al_2O_3,SiO_2 and MgO show quite different activities and selectivities for oxygenates and ethane in ethylene hydroformylation.

不同MgO载体对合成低碳烯烃用铁锰基催化剂的影响

采用共沉淀法、硝酸盐热分解法制备的MgO和商品MgO为载体，使用共浸渍法制备了系列FeMn／MgO催化剂，以CO加氢合成低碳烯烃为模型反应，对小同催化剂的反应性能进行了考察，采用X射线光电子能谱、N2物理吸附、X射线物相分析、程序升温还原等表征技术对催化剂的结构和性能进行了表征。结果表明，采用共沉淀法制备的MgO载体比表面积最大，达到203．5m^2／g，以此为载体制备的催化剂取得了最优的CO加氢合成低碳烯烃性能。在340℃、2．0MPa、1600h^-1的反应条件下，CO转化率达到91．36％，C2^=～C4^=选择性为58．48％。催化剂的比表面积大，活性组分分布均匀且在表面含量高及低温还原性能的明显改善是其具有优异的催化性能的重要原因。

MgO/γ-Al_2O_3烷氧基化催化剂制备及结构与性能研究

在γ Al2 O3 载体上浸渍Mg (NO3 ) 2 ·6H2 O ,然后分别经 40 0、45 0和 5 0 0℃焙烧制成MgO/γ Al2 O3 固体碱催化剂。结果表明 ,MgO在γ Al2 O3 载体表面具有单层分散性质 ,当MgO的负载量低于某一数值 (阈值 )时 ,从样品的X光粉末衍射谱图上观察不到MgO的特征衍射峰 ,负载量超过阈值时开始出现MgO的晶相 ,且MgO的XRD衍射峰强度随MgO的负载量的增加而增加 ,其单分散阈值为 0 0 80 gMgO/ 10 0m2 γ Al2 O3 。应用CO2 TPD技术测定了样品的碱性 ,结果表明 ,样品在接近阈值时其碱量大幅度增加 ,碱强度提高。样品的比表面最初随着MgO负载量的增加而下降 ,但达阈值后基本保持不变。