Hydrodesulfurization over supported monometallic, bimetallic and promoted carbide and nitride catalysts

The preparation of alumina-supported β-Mo₂C, MoC_1−x (x≈0.5), γ-Mo₂N, Co–Mo₂C, Ni₂Mo₃N, Co₃Mo₃N and Co₃Mo₃C catalysts is described and their hydrodesulfurization (HDS) catalytic properties are compared to conventional sulfide catalysts having similar metal loadings. Alumina-supported β-Mo₂C and γ-Mo₂N catalysts (Mo₂C/Al₂O₃ and Mo₂N/Al₂O₃, respectively) are significantly more active than sulfided MoO₃/Al₂O₃ catalysts, and X-ray diffraction, pulsed chemisorption and flow reactor studies of the Mo₂C/Al₂O₃ catalysts indicate that they exhibit strong resistance to deep sulfidation. A model is presented for the active surface of Mo₂C/Al₂O₃ and Mo₂N/Al₂O₃ catalysts in which a thin layer of sulfided Mo exposing a high density of sites forms at the surface of the alumina-supported β-Mo₂C and γ-Mo₂N particles under HDS conditions. Cobalt promoted catalysts, Co–Mo₂C/Al₂O₃, have been found to be substantially more active than conventional sulfided Co–MoO₃/Al₂O₃ catalysts, while requiring less Co to achieve optimal HDS activity than is observed for the sulfide catalysts. Alumina-supported bimetallic nitride and carbide catalysts (Ni₂Mo₃N/Al₂O₃, Co₃Mo₃N/Al₂O₃, Co₃Mo₃C/Al₂O₃), while significantly more active for thiophene HDS than unpromoted Mo nitride and carbide catalysts, are less active than conventional sulfided Ni–Mo and Co–Mo catalysts prepared from the same oxidic precursors.     

Simultaneous hydrodesulfurization of thiophene and hydrogenation of cyclohexene over dimolybdenum nitride catalysts

A series of unsupported dimolybdenum nitride (γ-Mo₂N) catalysts differing in surface area were prepared by temperature programmed reduction of MoO₃ with a mixture of NH₃:N₂ (90:10). Characterization of catalysts by BET, XRD, TPR and XPS techniques was carried out. The samples were used as catalysts in hydrotreating reactions (simultaneous hydrodesulfurization of thiophene and hydrogenation of cyclohexene). Low surface area γ-Mo₂N materials show much higher specific conversions than those with higher surface area. These results indicate that HDS and HYD reactions over γ-Mo₂N seem to be structure-sensitive. The relative exposure extent of crystalline planes (1 1 1) and (2 0 0) over the different catalysts can be associated with their hydrogen adsorption capacities and with their catalytic performances. The catalytic activities are significantly affected by the catalyst pretreatment conditions.     

K/Ni/β-Mo2C: A highly active and selective catalyst for higher alcohols synthesis from CO hydrogenation

Nickel and potassium promoted β-Mo₂C catalysts were prepared for CO hydrogenation to higher alcohols synthesis. The results revealed that β-Mo₂C produced mainly hydrocarbons, but the addition of potassium resulted in a remarkable selectivity shift from hydrocarbons to alcohols over β-Mo₂C. Moreover, it was found that potassium enhanced the ability of chain propagation of β-Mo₂C catalyst and led to a higher selectivity to C₂⁺OH. The addition of nickel further enhanced higher alcohols synthesis, which showed the optimum at 1/8–1/6 of Ni/Mo molar ratios. The characterization suggested that there might be a synergistic effect of potassium and nickel on β-Mo₂C, which favored the alcohols synthesis. The production of alcohols appeared to be relevant to the presence of Mo⁴⁺ species, whereas the formation of hydrocarbons was closely associated with Mo²⁺ and/or Mo⁰ species on the surface of β-Mo₂C-based catalysts.     

Palladium–vanadium interaction in binary supported catalysts

We have studied the activity and selectivity of Pd/γ-Al₂O₃, VO_x/γ-Al₂O₃ and Pd–VO_x/γ-Al₂O₃ catalysts for the decomposition of NO and the reduction of NO with CO. Pd–VO_x/γ-Al₂O₃ catalysts were prepared by anchoring Pd(AcAc)₂ on VO_x/γ-Al₂O₃. Characterization of the binary samples by hydrogen chemisorption and TPR measurements indicated that the reduction of VO_x is enhanced by a close contact with palladium and that partially reduced vanadia decorate noble metal particles. This palladium–vanadium interaction alters the catalytic properties of palladium: the activity for NO decomposition is higher for the binary sample and, for the NO–CO reaction, both the activity and the selectivity to N₂ increase when vanadium is in contact with palladium.     

Synthesis of platinum–tin/alumina reforming catalysts from a well-defined platinum–tin precursor complex

The complex [(CH₃)₄N]₃[Pt(SnCl₃)₅] was selected as a molecular precursor to prepare PtSn/γ_c-Al₂O₃ reforming catalysts. The spectroscopic fingerprints of the starting complex were obtained by ¹⁹⁵Pt and ¹¹⁹Sn NMR and diffuse reflectance UV–visible spectroscopy. A series of supported catalysts were synthesized by wet impregnation of alumina with a solution of the precursor in acetone.

Well-dispersed species are obtained for Pt loadings below 1 wt.%; at higher loadings, a second species is formed that has spectroscopic features reminiscent of the initial complex and precipitates as a separate phase. Apparently, the Pt–Sn bonds are hydrolyzed in the low-loading species and preserved in the high-loading species.

The thermal transformations of PtSn/γ_c-Al₂O₃ catalysts are also studied and compared with those of the bulk precursor. In particular, it is shown that the nature of the atmosphere of thermal treatment (neutral or oxidizing) can orient the final catalyst towards preservation of an intimate Pt–Sn interaction, or towards demixtion.     

Effect of phosphorus addition on the hydrotreating activity of NiMo/Al2O3 carbide catalyst

A series of phosphorus promoted γ-Al₂O₃ supported NiMo carbide catalysts with 0–4.5 wt.% P, 13 wt.% Mo and 2.5 wt.% Ni were synthesized and characterized by elemental analysis, pulsed CO chemisorption, BET surface area measurement, X-ray diffraction, near-edge X-ray absorption fine structure, DRIFT spectroscopy of CO adsorption and H₂ temperature programmed reduction. X-ray diffraction patterns and CO uptake showed the P addition to NiMo/γ-Al₂O₃ carbide, increased the dispersion of β-Mo₂C particles. DRIFT spectra of adsorbed CO revealed that P addition to NiMo/γ-Al₂O₃ carbide catalyst not only increases the dispersion of Ni-Mo carbide phase, but also changes the nature of surface active sites. The hydrodenitrogenation (HDN) and hydrodesulfurization (HDS) activities of these P promoted NiMo/γ-Al₂O₃ carbide catalysts were performed in trickle bed reactor using light gas oil (LGO) derived from Athabasca bitumen and model feed containing quinoline and dibenzothiophene at industrial conditions. The P added NiMo/γ-Al₂O₃ carbide catalysts showed enhanced HDN activity compared to the NiMo/γ-Al₂O₃ catalysts with both the feed stocks. The P had almost no influence on the HDS activity of NiMo/γ-Al₂O₃ carbide with LGO and dibenzothiophene. P addition to NiMo/γ-Al₂O₃ carbide accelerated CN bond breaking and thus increased the HDN activity.     

Iminium cations as intermediates in the hydrodenitrogenation of alkylamines over sulfided NiMo/γ-Al2O3

The mechanism of the hydrodenitrogenation of the mixed dialkyl- and trialkylamines C₁NHC₆ and C₁N(C₆)₂ was studied over sulfided NiMo/γ-Al₂O₃ at 280 °C and 3 MPa. C₁NHC₆ reacted by disproportionation to C₁N(C₆)₂ as well as C₆N(C₁)₂ and by substitution by H₂S to methylamine and hexanethiol as well as hexylamine and methanethiol. C₁N(C₆)₂ reacted by substitution with H₂S to C₁NHC₆ and C₆NHC₆ and methane- and hexanethiol. The probability of breaking the C₁N bond was only slightly smaller than of breaking the C₆N bond in C₁N(C₆)₂. In the reaction of an equimolar mixture of C₅NHC₅ and C₁N(C₆)₂ both C₁N(C₅)₂ and C₆N(C₅)₂ were formed. The transfer of the methyl group in these reactions cannot be explained by imine and enamine intermediates, only iminium cation intermediates can explain all the products in the hydrodenitrogenation of monoalkyl-, dialkyl- and trialkylamines.     

Preparation of Au/TiO2 catalysts from Au(I)–thiosulfate complex and study of their photocatalytic activity for the degradation of methyl orange

Gold loaded on TiO₂ (Au/TiO₂) catalysts were prepared using Au(I)–thiosulfate complex (Au(S₂O₃)₂³⁻) as the gold precursor for the first time. The samples were characterized by UV–vis diffuse reflectance spectra, X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic absorption flame emission spectroscopy (AAS), and X-ray photoelectron spectroscopy (XPS) methods. Using Au(S₂O₃)₂³⁻ as gold precursor, ultra-fine gold nanoparticles with a highly disperse state can be successfully formed on the surface of TiO₂. The diameter of Au nanoparticles increases from 1.8 to 3.0 nm with increasing the nominal Au loading from 1% to 8%. The photocatalytic activity of Au/TiO₂ catalysts was evaluated from the analysis of the photodegradation of methyl orange (MO). With the similar Au loading, the catalysts prepared with Au(S₂O₃)₂³⁻ precursor exhibit higher photocatalytic activity for methyl orange degradation when compared with the Au/TiO₂ catalysts prepared with the methods of deposition–precipitation (DP) and impregnation (IMP). The preparation method has decisive influences on the morphology, size and number of Au nanoparticles loaded on the surface of TiO₂ and further affects the photocatalytic activity of the obtained catalysts.     

TPD and XRD studies of molybdenum nitride and its activity for hydrodenitrogenation of carbazole

The nitrided MoO₃ catalysts formed using two kinds of treatment with either NH₃ or He after nitriding were studied by temperature-programmed desorption and X-ray diffraction analyses. The catalysts were cooled to room temperature in either flowing NH₃ or He (NH or HE catalyst) after nitriding at 773, 973 and 1173 K with NH₃. The activities of the catalysts were determined during the hydrodenitrogenation of carbazole at 573 K and 10.1 MPa total pressure. MoO₂, γ-Mo₂N, and Mo metal were mainly formed in the NH catalysts nitrided at 773, 973 and 1173 K, respectively. Mo oxides and metals in the NH catalysts were nitrided to γ-Mo₂N and β-Mo₂N_0.78 with low crystallinity during TPD. The surface area of the NH and HE catalysts nitrided at 773 K increased to 66 and 59 m² g⁻¹ maximum from 1.1 m² g⁻¹ of fresh MoO₃, respectively, but decreased as the nitriding temperature increased to 973 K and 1173 K. The HE catalysts per surface area were more active than the NH catalysts for both the overall HDN reaction and hydrogenation, and the 1173 K-nitrided catalysts were highest. On the other hand, the NH catalysts were more active than the HE catalysts for C–N hydrogenolysis and the 973 K-nitrided catalyst showed a maximum activity for C–N hydrogenolysis.     

K2CO3/γ-A12O3催化剂在棉籽油制备生物柴油中的应用

利用等体积浸渍法制备K₂CO₃/γ-A1₂O₃负载型固体碱催化剂,应用于棉籽油和甲醇酯交换反应制备生物柴油。对催化剂使用前的保存条件、水分、重复使用性能、游离脂肪酸影响以及失活和再生进行了分析。结果表明,固体催化剂K₂CO₃/γ-Al₂O₃具有较好的抗水性,酸度对催化剂影响明显,重复使用4次未经活化的催化剂,催化活性明显降低,催化剂应密封保存。K₂CO₃/γ-A1₂O₃负载型固体碱催化剂经济实惠且催化效果良好。     

Preparation of new solid superacid catalyst, zirconium sulfate supported on γ-alumina and activity for acid catalysis

Zirconium sulfate supported on γ-Al₂O₃ catalysts were prepared by impregnation of powdered γ-Al₂O₃ with zirconium sulfate aqueous solution followed by calcining in air at high temperature. For Zr(SO₄)₂/γ-Al₂O₃ samples, no diffraction line of zirconium sulfate was observed up to 50 wt.%, indicating good dispersion of Zr(SO₄)₂ on the surface of γ-Al₂O₃. The acidity of catalysts increased in proportion to the zirconium sulfate content up to 40 wt.% of Zr(SO₄)₂. 40-Zr(SO₄)₂/γ-Al₂O₃ calcined at 400 °C exhibited maximum catalytic activities for 2-propanol dehydration and cumene dealkylation. The catalytic activities for both reactions, 2-propanol dehydration and cumene dealkylation were correlated with the acidity of catalysts measured by ammonia chemisorption method.     

Combination of non-thermal plasma and heterogeneous catalysis for oxidation of volatile organic compounds: Part 2. Ozone decomposition and deactivation of γ-Al2O3

The role of ozone was studied for two different configurations combining non-thermal plasma (NTP) and heterogeneous catalysis, namely the use of a gas phase plasma with subsequent exposure of the effluent to a catalyst in a packed-bed reactor (post-plasma treatment) and the placement of the catalyst directly in the discharge zone (in-plasma catalysis). Non-porous and porous alumina and silica were deployed as model catalysts. The oxidation of immobilised hydrocarbons, toluene as a volatile organic compound and CO as an inorganic pollutant were studied in both operational modes.

While conversion and selectivity of hydrocarbon oxidation in the case of catalytic post-plasma treatment can be fully explained by the catalytic decomposition of O₃ on γ-Al₂O₃, the conversion processes for in-plasma catalysis are more complex and significant oxidation was also measured for the other three materials (-Al₂O₃, quartz and silica gel). It became obvious that additional synergetic effects can be utilised in the case of in-plasma catalysis due to short-lived species formed in the NTP.

The capability of porous alumina for ozone decomposition was found to be correlated with its activity for oxidation of carbon-containing agents. It could be clearly shown that the reaction product CO₂ poisons the catalytic sites at the γ-Al₂O₃ surface. The catalytic activity for O₃ decomposition can be partially re-established by NTP treatment. However, for practical purposes the additional reaction pathways provided by in-plasma catalytic processes are essential for satisfactory conversion and selectivity.     

Performance and characterization of Ru/Al2O3 and Ru/SiO2 catalysts modified with Mn for Fischer–Tropsch synthesis

Mn effect and characterization on γ-Al₂O₃-, -Al₂O₃- and SiO₂-supported Ru catalysts were investigated for Fischer–Tropsch synthesis under pressurized conditions. In the slurry phase Fischer–Tropsch reaction, γ-Al₂O₃ catalysts showed higher performance on CO conversion and C₅⁺ selectivity than -Al₂O₃ and SiO₂ catalysts. Moreover, Ru/Mn/γ-Al₂O₃ exhibited high resistance to catalyst deactivation and other catalysts were deactivated during the reaction. From characterization results on XRD, TPR, TEM, XPS and pore distribution, Ru particles were clearly observed over the catalysts, and γ-Al₂O₃ catalysts showed a moderate pore and particle size such as 8 nm, where -Al₂O₃ and SiO₂ showed highly dispersed ruthenium particles. The addition of Mn to γ-Al₂O₃ enhanced the removal of chloride from RuCl₃, which can lead to the formation of metallic Ru with moderate particle size, which would be an active site for Fischer–Tropsch reaction. Concomitantly, manganese chloride is formed. These schemes can be assigned to the stable nature of Ru/Mn/γ-Al₂O₃ catalyst.     

CVD preparation of alumina-supported niobium nitride and its activity for thiophene hydrodesulfurization

Niobium nitride was synthesized on a Si(400) substrate and a γ-alumina pellet using a CVD method with a stream of NbCl₅/Ar, NH₃, and H₂ gases at 723–973 K under reduced pressure. The composition and surface properties of the deposited niobium nitride were analyzed using XRD and XPS measurements. The activity of alumina-supported niobium nitrides for the hydrodesulfurization (HDS) of thiophene at 673 K and atmospheric pressure was determined. The alumina had a surface area of 177 m² g⁻¹ and the alumina-supported niobium nitride catalyst had surface areas of 179–190 m² g⁻¹. Although the catalysts had low activity in the initial stages, the activity increased after 200–300 min started to about three times the initial activities. XPS analysis indicated that the activity of the niobium nitride catalysts was decreased by sulfur accumulation on the surface and nitrogen released from niobium nitride. The relationship between the surface properties of the niobium nitride catalysts and the activities for thiophene HDS is discussed.     

Surface properties and reactivity of Cu/γ-Al2O3 catalysts for NO reduction by C3H6: Influences of calcination temperatures and additives

The influences of calcination temperatures and additives for 10 wt.% Cu/γ-Al₂O₃ catalysts on the surface properties and reactivity for NO reduction by C₃H₆ in the presence of excess oxygen were investigated. The results of XRD and XPS show that the 10 wt.% Cu/γ-Al₂O₃ catalysts calcined below 973 K possess highly dispersed surface and bulk CuO phases. The 10 wt.% Cu/γ-Al₂O₃ and 10 wt.% Mn–10 wt.% Cu/γ-Al₂O₃ catalysts calcined at 1073 K possess a CuAl₂O₄ phase with a spinel-type structure. In addition, the 10 wt.% La–10 wt.% Cu/γ-Al₂O₃ catalyst calcined at 1073 K possesses a bulk CuO phase. The result of NO reduction by C₃H₆ shows that the CuAl₂O₄ is a more active phase than the highly dispersed and bulk CuO phase. However, the 10 wt.% Mn–10 wt.% Cu/γ-Al₂O₃ catalyst calcined at 1073 K possesses significantly lower reactivity for NO reduction than the 10 wt.% Cu/γ-Al₂O₃ catalyst calcined at 1073 K, although these catalysts possess the same CuAl₂O₄ phase. The low reactivity for NO reduction for 10 wt.% Mn–10 wt.% Cu/γ-Al₂O₃ catalyst calcined at 1073 K is attributed to the formation of less active CuAl₂O₄ phase with high aggregation and preferential promotion of C₃H₆ combustion to CO_x by MnO₂. The engine dynamometer test for NO reduction shows that the C₃H₆ is a more effective reducing agent for NO reduction than the C₂H₅OH. The maximum reactivity for NO reduction by C₃H₆ is reached when the NO/C₃H₆ ratio is one.     

A comparison between β- and USY-zeolite-based hydrocracking catalysts

Two series of zeolite-based hydrocracking catalysts were prepared to study the effects of the support type, preparation method and metal loading on catalyst properties and hydrocracking activity for hydrotreated vacuum gas oil (HT-VGO). The support used was γ-Al₂O₃ and β-zeolite in the first series and γ-Al₂O₃ and USY-zeolite in the second series. Nickel and tungsten were loaded as active metals on these supports. The prepared catalysts were characterized as to their surface area, pore volume, thermal stability, reducibility and acidity characteristics. The characterization results revealed that catalysts displayed significant differences in properties dependent on the preparation method and the type of support used. Catalysts from both series showed promising results for HT-VGO hydrocracking in the batch reactor. A correlation exists between the reducibility of oxidic form and the hydrogenation activity of the sulfided form of the catalysts. The higher the reducibility, the higher the hydrogenation activity. Catalysts prepared on mixed supports gave higher amounts of saturates.     

Fischer–Tropsch synthesis on monolithic catalysts of different materials

Monolithic structures made of cordierite, γ-Al₂O₃ and steel have been prepared as catalysts and tested for Fischer–Tropsch activity. The monoliths made of cordierite and steel were washcoated with a 20 wt.% Co–1 wt.% Re/γ-Al₂O₃ Fischer–Tropsch catalyst whereas the γ-Al₂O₃ monoliths were made by direct impregnation with an aqueous solution of the Co and Re salts resulting in a loading of 12 wt.% Co and 0.5 wt.% Re. The activity and selectivity of the different monoliths were compared with the corresponding powder catalysts.

Higher washcoat loadings resulted in decreased C₅₊ selectivity and olefin/paraffin ratios due to increased transport limitations. The impregnated γ-Al₂O₃ monoliths also showed similar C₅₊ selectivities as powder catalysts of small particle size (38–53 μm). Lower activities were observed with the steel monoliths probably due to experimental problems.     

CuO含量对Pd/Al2O3催化剂乙醇氧化性能的影响

采用浸渍法制备了一系列具有不同CuO含量的Pd-CuO/Al₂O₃催化剂，并将其用于乙醇氧化反应，其结构与性质通过XRD、H₂-TPR和NH₃-TPD等手段进行分析。结果发现，催化剂的活性并不是随着CuO含量的增加而增强，Pd-1.0%CuO/Al₂O₃催化剂表现出最佳的活性，其点火温度和完全转化温度比Pd/Al₂O₃催化剂至少降低了50℃。与Pd/Al₂O₃催化剂相比，含CuO催化剂增强的衍射峰强度以及氢化钯分解峰的消失，说明Pd-Cu合金结构的形成有利于Pd、Cu物种之间的协同作用。对于Pd-1.0%CuO/Al₂O₃催化剂来说，还原峰向低温的移动以及还原峰面积的增大说明该催化剂上氧化性物质更易被还原且数量在增加，这对于氧化反应是十分有利的，新出现的还原峰表示Pd、Cu的相互作用生成了新物种。NH₃-TPD结果中更高含量的低温酸有利于高活性，而且新出现的脱附峰说明形成了新的酸性位点。     

η-Al2O3与γ-Al2O3在CS2催化水解反应中的性能比较

通过制备高纯度的前驱体湃铝石获得了η-Al₂O₃材料,采用XRD验证了η-Al₂O₃与γ-Al₂O₃在晶相结构上的差异,比较了两者的表面形貌、织构及酸碱性能,结果显示,η-Al₂O₃与γ-Al₂O₃的比表面积相当,但η-Al₂O₃具有更弱的弱碱位和较少的强碱位,并拥有丰富的中等强度酸性位。将η-Al₂O₃与γ-Al₂O₃作为催化剂应用于CS₂水解反应,结果表明,在(200~450) ℃测试温度范围内,η-Al₂O₃催化剂对CS₂的水解活性始终优于γ-Al₂O₃,两种催化剂上CS₂反应的浓度效应也明显不同,推测与它们的酸碱性质影响了对CS₂的吸附能力有关,导致两者催化CS₂水解反应遵循了不同的机制。     

低成本大比表面积γ-Al2O3的制备

以廉价无机铝盐硫酸铝为原料,氨水为沉淀剂,十二烷基硫酸钠为添加剂,采用简单沉淀法制备得到较大比表面积γ-Al₂O₃。通过N₂低温物理吸附-脱附、X射线衍射、红外光谱、热重、元素分析、扫描及透射电镜等,研究制备过程中沉淀温度、溶液pH值和添加剂用量对产物γ-Al₂O₃及其前驱体的晶相结构、形貌织构等性质的影响。结果表明,在沉淀温度75 ℃、硫酸铝浓度0.25 mol·L^-1、溶液pH=9.0、老化时间12 h和n(十二烷基硫酸钠)∶n[Al₂(SO₄)₃]=0.375∶1条件下,所得前驱体(拟薄水铝石)经600 ℃焙烧后,可获得大比表面积(416.65 m²·g^-1)γ-Al₂O₃,并且样品中因十二烷基硫酸钠添加,引入的S及Na等杂质含量极少。