镍助剂对碳化钼催化剂的二苯并噻吩加氢脱硫性能的影响

 将MoO3和Ni-Mo混合氧化物在CH4/H2气氛中程序升温还原碳化制备了相应的碳化钼和碳化镍钼催化剂, X射线粉末衍射表征其物相分别为β-Mo2C和Ni-Mo2C. 考察了Ni助剂对碳化钼催化剂的制备及二苯并噻吩加氢脱硫反应性能的影响. 结果表明, Ni助剂的加入降低了碳化钼催化剂所需的还原碳化温度,提高了催化剂的比表面积,并对其二苯并噻吩加氢脱硫反应活性有明显的促进作用. Ni助剂添加量以Ni/Mo原子比为0.3为宜,此时Ni和Mo之间的催化协同效应达到最佳. 当反应压力为3.0 MPa, 反应温度为330 ℃, 空速8 h-1, H2/原料液体积比为500∶1时, 625 ℃还原碳化制备的碳化镍钼催化剂对0.6%二苯并噻吩/环己烷溶液的二苯并噻吩转化率达到96.25%, 较相应的碳化钼催化剂提高了1.57倍.     

Ni–Mo2C supported on alumina as a substitute for Ni–Mo reduced catalysts supported on alumina material for dry reforming of methane

In this study, alumina-supported NiMo catalysts were carburized to obtain alumina-supported nickel–molybdenum carbides as potential catalysts for dry reforming of methane. The typical carbide was compared with a low carburized material (in 5% H₂/CH₄) and a reduced NiMo catalyst. It was shown that the passivated alumina-supported NiMo catalysts by carbon lead to higher reactivity, selectivity, and stability for dry methane reforming reaction.     

Phenolic resin as a carbon source for the synthesis of monometallic Mo and bimetallic CoMo carbides via carbothermal reduction route

It was the first time that phenolic resin (PR) was used as a carbon source for the synthesis of nanostructured monometallic Mo and bimetallic CoMo carbides via carbothermal reduction route. The results showed that phase-pure β-Mo₂C can be formed under an Ar atmosphere at 900°C or a H₂ atmosphere above 700°C. However, almost pure CoMo carbides (Co₃Mo₃C and Co₆Mo₆C) can be obtained only under a H₂ atmosphere at a low temperature of 630°C for 24 and 48 h, respectively. The role of PR in the preparation process has been investigated and a detailed formation mechanism was proposed based on the experimental results.     

XPS study of potassium-promoted molybdenum carbides for mixed alcohols synthesis via CO hydrogenation

The X-ray photoelectron spectroscopy (XPS) was used to investigate the surface characteristic of potassium-promoted or un-promoted both β-Mo_2C and α-MoC_(1-x) pretreated by syngas at different temperatures, and the promotional effect of potassium on the catalytic performance was also studied. XPS results revealed that the content of surface Mo and its valence distribution between β-Mo_2C and α-MoC_(1-x) were quite different. Promoted by potassium, the remarkable changes were observed for surface composition and valence of Mo distribution over β-Mo_2C. Potassium had strong electronic effect on β-Mo_2C, which led to a higher Mo~(4+) content. On the contrary, potassium had little electronic effect on α-MoC_(1-x), and K-Mo interaction was weak. Therefore, Mo~0 and Mo~(2+) became the dominant species on the catalyst surface, and the Mo~(4+) content showed almost no increase as the pretreatment temperature enhanced. In terms of catalytic performance of molybdenum carbides, the increase in Mo~0 most likely explained the increase in hydrocarbon selectivity, yet Mo~(4+) might be responsible for the alcohols synthesis.     

Dynamics of topochemical reactions in supported iron Fischer–Tropsch synthesis catalysts during their reduction in flowing CO and CO + H<Subscript>2</Subscript>

The reduction of Fe₂O₃/SiO₂ catalysts in flowing CO and CO + H₂ in the temperature-programmed and isothermal modes has been investigated by in situ magnetization measurements. The process takes place in two steps, successively yielding magnetite and Hägg carbide. The carbide concentration in the case of reduction with CO is higher than in the case of reduction with the CO + H₂. This is assumed to be due to the formation of Fe₂SiO₄ in the reduction of the catalysts with CO + H₂.     

Study on chemisorption of H<Subscript>2</Subscript>, O<Subscript>2</Subscript>, CO and C<Subscript>2</Subscript>H<Subscript>4</Subscript>on Pt-Ag/SiO<Subscript>2</Subscript>catalysts by microcalorimetry and FTIR

Adsorption microcalorimetry has been employed to study the interaction of ethylene with the reduced and oxidized Pt-Ag/SiO₂catalysts with different Ag contents to elucidate the modified effect of Ag towards the hydrocarbon processing on platinum catalysts. In addition, microcalorimetric adsorption of H₂, O₂, CO and FTIR of CO adsorption were conducted to investigate the influence of Ag on the surface structure of Pt catalyst. It is found from the microcalorimetric results of H₂and O₂adsorption that the addition of Ag to Pt/SiO₂leads to the enrichment of Ag on the catalyst surface which decreases the size of Pt surface ensembles of Pt-Ag/SiO₂catalysts. The microcalorimetry and FTIR of CO adsorption indicates that there still exist sites for linear and bridged CO adsorption on the surface of platinum catalysts simultaneously although Ag was incorporated into Pt/SiO₂. The ethylene microcalorimetric results show that the decrease of ensemble size of Pt surface sites suppresses the formation of dissociative species (ethylidyne) upon the chemisorption of C₂H₄on Pt-Ag/SiO₂. The differential heat vs. uptake plots for C₂H₄adsorption on the oxygen-preadsorbed Pt/SiO₂and Pt-Ag/SiO₂catalysts suggest that the incorporation of Ag to Pt/SiO₂could decrease the ability for the oxidation of C₂H₄.     

Study of reduced Mo/Al2O3 metathesis catalysts prepared via metal complexes

The Mo/Al₂O₃ catalysts for propene metathesis were prepared both via anchoring Mo complexes of various nuclearities and by conventional method of impregnation. The catalysts from metal complexes were found to be active in metathesis at ambient temperature after reduction with H₂ or CO at 400–500°C. The average oxidation state of Mo in the activated catalysts was determined with regard to oxygen consumption needed for oxidation of the reduced Mo species to Mo⁶⁺.     

Synthesis and characterization of molybdenum carbides using propane as carbon source

Bulk face-centered-cubic (fcc)-based η-MoC_1−x and hexagonal-close-packed (hcp)-based β-Mo₂C have been prepared using C₃H₈/H₂ by temperature-programmed reaction method and a rapid heating method. In this work, direct carburization of MoO₃ produces η-MoC_1−x or MoO_xC_y with excess carbon, different from that with CH₄/H₂ or C₂H₆/H₂ as carburization reagent. A successive post-treatment by hydrogen causes the phase transformation from fcc-based η-MoC_1−x or MoO_xC_y to hcp-based β-Mo₂C. Amorphous SiO₂-supported β-Mo₂C is also successfully prepared by the two methods and passes through the same route as the bulk one. HRTEM, BET surface area measurements and thiophene hydrodesulfurization reaction are conducted for the comparison of the two methods. The results indicate that different ramping rates bring slight difference in specific surface area and initial catalytic activity but obvious difference in particle size to the final product supported β-Mo₂C.     

Bifunctional catalysis of Mo/HZSM-5 in the dehydroaromatization of methane with CO/CO2 to benzene and naphthalene

The catalytic dehydrocondensation of methane to aromatics such as benzene and naphthalene was studied on the Mo carbide catalysts supported on micro- and mesoporous materials such as HZSM-5 (0.6 nm) and FSM-16 (2.7 nm). The Mo catalysts supported on H-ZSM-5 having appropriate micropores (0.6 nm size) and Si/Al ratios (20-70) exhibit higher yields (90-150 nmol/g-cat/s) and selectivities (higher than 74% on the carbon basis) in methane conversion to aromatic products such as benzene and naphthalene at 973 K and 1 atm, although they are drastically deactivated because of substantial coke formation. It was demonstrated that the CO/CO₂ addition to methane effectively improves the catalyst performance by keeping a higher methane conversion and selectivities of benzene formation in the prolonged time-on-stream. The oxygen derived from CO and CO₂ dissociation suppresses polycondensation of aromatic products and coke formation in the course of methane conversion. XAFS and TG/DTA/mass-spectrometric studies reveal that the zeolite-supported Mo oxide is endothermally converted under the action of methane around 955 K to nanosized particles of molybdenum carbide (Mo₂C) (Mo-C, coordination number = 1,R- 2.09 å; Mo-Mo, coordination number = 2.3–3.5;R = 2.98 å). The SEM pictures showed that the nanostructured Mo carbide particles are highly dispersed on and inside the HZSM-5 crystals. On the other hand, it was demonstrated by IR measurements of pyridine adsorption that the Mo/HZSM-5 catalysts having the optimum SiO₂/Al₂O₃ ratios around 40 show the maximum Brönsted acidity among the catalysts with the SiO₂/Al₂O₃ ratios of 20–1900. There is a close correlation between the activity of benzene formation in the methane aromatization and the Brönsted acidity of HZSM-5 due to the bifunctional catalysis.     

The influence of phase and morphology of molybdenum nitrides on ammonia synthesis activity and reduction characteristics

The reactivities of a series of ternary and binary molybdenum nitrides have been compared. Data have been obtained for the catalytic synthesis of ammonia at 400 °C and ambient pressure using a 3:1 H₂:N₂ mixture. Amongst the ternary nitrides, the mass normalised activity is in the order Co₃Mo₃N>Fe₃Mo₃N?Ni₂Mo₃N. For the binary molybdenum nitrides, the ammonia synthesis activity is significantly lower than that of Co₃Mo₃N and Fe₃Mo₃N and varies in the order γ-Mo₂N∼β-Mo₂N_0.78?δ-MoN. Nanorod forms of β-Mo₂N_0.78 and γ-Mo₂N exhibit generally similar activities to conventional polycrystalline samples, demonstrating that the influence of catalyst morphology is limited for these two materials. In order to characterise the reactivity of the lattice nitrogen species of the nitrides, temperature programmed reactions with a 3:1 H₂:Ar mixture at temperatures up to 700 °C have been performed. For all materials studied, the predominant form of nitrogen lost was N₂, with smaller amounts of NH₃ being formed. Post-reaction powder diffraction analyses demonstrated lattice shifts in the case of Co₃Mo₃N and Ni₂Mo₃N upon temperature programmed reaction with H₂/Ar. Incomplete decomposition yielding mixtures of Mo metal and the original phase were observed for Fe₃Mo₃N and γ-Mo₂N, whilst β-Mo₂N_0.78 transforms completely to Mo metal and δ-MoN is converted to γ-Mo₂N.     

Mo 和 Cu 助剂对 FeK/SiO2 催化剂费托合成性能的影响

 研究了 Mo 和 Cu 助剂对 FeK/SiO₂ 催化剂的性质及费托 (F-T) 合成性能的影响. 采用 N₂ 物理吸附、H₂ 程序升温还原、X 射线衍射、穆斯堡尔谱和 X 射线光电子能谱技术对催化剂进行了表征. 结果表明, Mo 加入后与 Fe 产生了较强的相互作用, 抑制了催化剂的还原和碳化; Cu 助剂的加入促进了催化剂的还原和碳化; 当 Mo 和 Cu 共同加入后, 催化剂的还原和碳化行为与单独加入 Cu 助剂时相似. 催化剂 F-T 合成性能在固定床上于 280 ^oC, 1.5 MPa, 2 000 h^-1, H₂/CO = 2.0 的合成气中测试. 结果表明, Mo 的加入降低了催化剂活性, 但提高了重质烃 (C₅₊) 的选择性; Cu 的添加提高了催化剂的活性, 但对稳定 C₅₊选择性作用不明显. Mo 和 Cu 共同加入后, 催化剂既表现出较为稳定的 C₅₊选择性, 同时其活性也没有降低.     

Effect of Pt nanoparticle size on the specific catalytic activity of Pt/SiO<Subscript>2</Subscript> and Pt/TiO<Subscript>2</Subscript> in the total oxidation of methane and <Emphasis Type="Italic">n</Emphasis>-butane

The dependence of the specific catalytic activity (A _sp ) of the catalysts Pt/SiO₂ and Pt/TiO₂ in the total oxidation of CH₄ and n-C₄H₁₀ on the Pt nanoparticle size (in the range from 1 to 4 nm) was studied. The specific catalytic activity increases with an increase in the platinum nanoparticle size, indicating that the total oxidation is a structure-sensitive reaction. The structure sensitivity depends on the size of an oxidized molecule: it increases sharply on going from CH₄ to n-C₄H₁₀. The support also exerts a considerable effect on the A _sp value: in the oxidation of both CH₄ and C₄H₁₀ the specific catalytic activity for the catalysts Pt/TiO₂ is 3–4 times that for Pt/SiO₂.     

钾调变Mo/SBA-15催化剂用于乙烷选择氧化制乙醛

采用两步浸渍法制备钾改性的Mo/SBA-15 催化剂. 采用N₂吸附,X射线衍射（XRD）,透射电镜（TEM）,紫外-可见（UV-Vis）吸收光谱,拉曼（Raman）光谱,NH₃程序升温脱附（NH₃-TPD）,CO₂程序升温脱附（CO₂-TPD）,H₂程序升温还原（H₂-TPR）等手段表征催化剂的物理化学性质. 研究结果表明,在Mo_0.75/SBA-15 中添加K之后,有新物种钾钼酸盐生成,并且当K/Mo的摩尔比不同时,钼物种的存在状态也不同. 添加钾之后,催化剂的活性和总醛（甲醛、乙醛、丙烯醛）的选择性均有所提高,并且受钾的添加量影响. 在575 ℃时,在K_0.25-Mo_0.75/SBA-15催化剂上醛的收率可高达8.5%（摩尔分数）.     

Highly efficient electrocatalytic hydrogen evolution promoted by O–Mo–C interfaces of ultrafine β-Mo2C nanostructures

Optimizing interfacial contacts and thus electron transfer phenomena in heterogeneous electrocatalysts is an effective approach for enhancing electrocatalytic performance. Herein, we successfully synthesized ultrafine β-Mo₂C nanoparticles confined within hollow capsules of nitrogen-doped porous carbon (β-Mo₂C@NPCC) and found that the surface layer of molybdenum atoms was further oxidized to a single Mo–O surface layer, thus producing intimate O–Mo–C interfaces. An arsenal of complementary technologies, including XPS, atomic-resolution HAADF-STEM, and XAS analysis clearly reveals the existence of O–Mo–C interfaces for these surface-engineered ultrafine nanostructures. The β-Mo₂C@NPCC electrocatalyst exhibited excellent electrocatalytic activity for the hydrogen evolution reaction (HER) in water. Theoretical studies indicate that the highly accessible ultrathin O–Mo–C interfaces serving as the active sites are crucial to the HER performance and underpinned the outstanding electrocatalytic performance of β-Mo₂C@NPCC. This proof-of-concept study opens a new avenue for the fabrication of highly efficient catalysts for HER and other applications, whilst further demonstrating the importance of exposed interfaces and interfacial contacts in efficient electrocatalysis.

Ultrafine β-Mo₂C nanostructures encapsulated in N-doped carbon capsules featuring O–Mo–C interfaces as the active sites for HER have been unveiled.     

Pechini synthesis and characterization of molybdenum carbide and nickel molybdenum carbide

Carbides, such as η-Ni₆Mo₆C, are considered as low-cost substitutes for noble metal catalysts for present applications in hydrodesulfurization and for a possible future sulfur-tolerant fuel cell anode catalyst. Most synthesis methods set the carbon content of the carbides by a carbon-based atmosphere or solid carbon in the synthesis. We show here that β-Mo₂C and η-Ni₆Mo₆C can be synthesized using a Pechini process, simply by heating metal acetates mixed with citric acid and ethylene glycol in one step under H₂ with the only source of carbon being the precursor solution. The β-Mo₂C forms when heating a Mo-acetate precursor at 850 °C. When using Ni- and Mo-acetates, β-Mo₂C forms at 700 °C and lower temperatures, while η-Ni₆Mo₆C forms during heating at 800-900 °C. The η-Ni₆Mo₆C has a surface area of 95.5 m² g⁻¹ and less than 10 m² g⁻¹ when prepared at 800 and 900 °C, respectively. Some Ni₃C, Ni, and NiC impurities are also present in the nanostructured η-Ni₆Mo₆C that was prepared at 900 °C. The η-Ni₆Mo₆C materials made by the Pechini process are compared with those made from a traditional synthesis, using metal organic precursors at 1000 °C under CO/CO₂ mixtures with a carbon activity of 0.011. Our results imply that H₂ and the Pechini process can be used to achieve carbon activities similar to those obtained by methods using gaseous or solid carbon sources.     

Promotion effect of adsorbed water/OH on the catalytic performance of Ag/activated carbon catalysts for CO preferential oxidation in excess H2

Activated carbon (AC) supported silver catalysts were prepared by incipient wetness impregnation method and their catalytic performance for CO preferential oxidation (PROX) in excess H₂ was evaluated. Ag/AC catalysts, after reduction in H₂ at low temperatures (≤200 °C) following heat treatment in He at 200 °C (He200H200), exhibited the best catalytic properties. Temperature-programmed desorption (TPD), X-ray diffraction (XRD) and temperature-programmed reduction (TPR) results indicated that silver oxides were produced during heat treatment in He at 200 °C which were reduced to metal silver nanoparticles in H₂ at low temperatures (≤200 °C), simultaneously generating the adsorbed water/OH. CO conversion was enhanced 40% after water treatment following heat treatment in He at 600 °C. These results imply that the metal silver nanoparticles are the active species and the adsorbed water/OH has noticeable promotion effects on CO oxidation. However, the promotion effect is still limited compared to gold catalysts under the similar conditions, which may be the reason of low selectivity to CO oxidation in PROX over silver catalysts. The reported Ag/AC-S-He catalyst after He200H₂00 treatment displayed similar PROX of CO reaction properties to Ag/SiO₂. This means that Ag/AC catalyst is also an efficient low-temperature CO oxidation catalyst.     

Thermogravimetric study of the carburization and coking of unsupported and carbon-supported Fe,Mo and Fe−Mo catalysts for fischer-tropsch synthesis

Carburization and coke deposition of unsupported and carbon-supported Fe, Mo and Fe?Mo catalysts in syngas have been studied using thermogravimetry. Compositions of the carbides formed are evaluated on the basis of the amount of metals in the catalysts and amount of carbon deposited during carburization. It is shown that carburization temperature and the nature of the carbides formed (Fe₅C₂ and Fe₂C for iron and Mo₂C for molybdenum) depend on the metals but are influenced by the support and metal loading. Coke deposition on these catalysts takes place as soon as carburization is complete.     

Pt的氧化状态对甲醇氧化活性的影响

采用NaBH4还原法制备了XC-72碳黑负载的Pt电催化剂,并在化学还原后用H2O2处理部分催化剂以改变Pt的氧化状态,以期改善Pt活性中心上水的离解而提高催化活性.X射线光电子能谱结果表明,经H2O2处理的催化剂含有较多的氧化态Pt.通过循环伏安法和记时电流法考察了经处理和未经处理的催化剂在酸性条件下的甲醇氧化的催化...     

Struktur und katalytische Eigenschaften von Molybdänoxid-Trägerkatalysatoren bei einigen Oxydationsreaktionen

Structure and Catalytic Properties of Molybdenum Oxide Supported Catalysts in Some Oxidation Reactions Molybdenum supported catalysts were prepared by using different precursor compounds such as Mo(π-C₃H₅)₄, [Mo(OC₂H₅)₅]₂, MoCl₅, (NH₄)₆Mo₇O₂₄, and their catalytic behaviour in some oxidation reactions was studied. During the preparation process, as a result of interaction between the molybdenum compound used and the support, different surface compounds with strongly differing catalytic properties have been formed. MoO₃ and supported catalysts with MoO₃ crystallites on the surface, catalyse the H₂ oxidation at temperatures above 400°C and the CO oxidation at temperatures of about 500°C. The reaction proceeds according to a redox mechanism. On surface compounds of molybdenum which exist on the surface if organic complexes are used as precursors, the catalytic H₂ oxidation occurs even at 100°C with a high reaction rate. The catalytic CO oxidation on these catalysts occurs at temperatures of about 300°C. An associative mechanism on coordinative unsaturated Mo^VI sites is discussed.     

Mechanism of CO oxidation in excess H2 over CuO/CeO2 catalysts: ESR and TPD studies

The oxidation of CO with oxygen over (0.25–6.4)% CuO/CeO₂ catalysts in excess H₂ is studied. CO conversion increases and the temperature range of the reaction decreases by 100 K as the CuO content is raised. The maximal CO conversion, 98.5%, is achieved on 6.4% CuO/CeO₂ at 150°C. At T > 150°C, the CO conversion decreases as a result of the deactivation of part of the active sites because of the dissociative adsorption of hydrogen. CO is efficiently adsorbed on the oxidized catalyst to form CO-Cu⁺ carbonyls on Cu₂O clusters and is oxidized by the oxygen of these clusters, whereas it is neither adsorbed nor oxidized on Cu⁰ of the reduced catalysts. The activity of the catalysts is recovered after the dissociative adsorption of O₂ on Cu⁰ at T ～ 150°C. The activation energies of CO, CO₂, and H₂O desorption are estimated, and the activation energy of CO adsorption yielding CO-Cu⁺ carbonyls is calculated in the framework of the Langmuir-Hinshelwood model.