Effects of zeolite structure and aluminum content on thiophene adsorption, desorption, and surface reactions

The adsorption and desorption of thiophene and the reactions of thiophene-derived adsorbed species in He, H₂, and O₂ were examined on H-ZSM5, H-Beta, and H-Y with varying Si/Al ratios. Thiophene adsorption uptakes (per Al) were independent of Al content, but were above unity and influenced by zeolite structure (1.7, 2.2, and 2.9 on H-ZSM5, H-Beta, and H-Y). These data indicate that thiophene oligomers form during adsorption and that their size depends on spatial constraints within zeolite channels. Adsorption and oligomerization occur on Brønsted acid sites at 363 K. Thiophene/toluene adsorption from their mixtures show significant thiophene selectivity ratios (10.3, 7.9, and 6.4, for H-ZSM5, H-Beta, and H-Y zeolites), which exceed those expected from van der Waals interactions and reflect specific interactions with Brønsted acid sites and formation of toluene–thiophene reaction products. Treatment of thiophene-derived adsorbed species above 363 K in He or H₂ led to depolymerization of thiophene oligomers and to the formation of unsaturated adsorbed species with a 1:1 thiophene/Al stoichiometry on all zeolites and at all Si/Al ratios. These unsaturated species desorb as stable molecules, such as H₂S, hydrocarbons, and larger organosulfur compounds, formed via ring opening and hydrogen transfer from H₂ or co-adsorbed species, and also form stranded unsaturated organic deposits. Smaller channels and higher Al contents preferentially formed H₂S, benzotiophenes, and arene products during treatment in He or H₂, as a result of diffusion-enhanced of secondary reactions of desorbed thiophene molecules with adsorbed thiophene-derived species. Only oxidative regeneration treatments led to full recovery of thiophene uptake capacities. A preceding treatment in H₂, however, led to the partial recovery of thiophene-derived carbon atoms as useful hydrocarbons and decreased the amount of CO₂ and SO₂ formed during subsequent oxidative treatments required for regeneration.     

NH3-TPD and XPS studies of Ru/Al2O3 catalyst and HDS activity

The effects of pretreatment of catalyst on its surface properties and the HDS activity of a 0.49% Ru/Al₂O₃ catalyst were studied in a single-pass, differential microreactor. The surface properties of the catalyst were measured by NH₃-TPD and XPS analysis. The Ru/Al₂O₃ catalyst was pretreated in three ways: reduced in H₂ (Ru-R catalyst), oxidized in air and subsequently reduced in H₂ (Ru-OR catalyst), or sulfided in H₂S/H₂ (Ru-S catalyst). Three types of peaks (low, middle, and high temperatures) were observed in the NH₃-TPD study. The predominant high-temperature peak was observed for both the Ru-OR and Ru-S catalyst, pretreated at 300°C. Mass spectrometry showed that the high-temperature peak in NH₃-TPD consisted of N₂ and H₂ formed from the decomposition of NH₃ on the ruthenium sites. NO adsorption of unsaturated Ru species was related to the low-temperature peak in the NH₃-TPD. The XPS analysis showed that the peaks at 279.9 eV, 280.6 eV, and 282.5 eV were ascribed to metallic ruthenium, RuO₂, and RuO₃, respectively. The low-, middle-, and high-temperature peaks were assigned to RuO₂, acid sites on alumina, and metallic Ru, respectively. Metallic ruthenium was effective in the HDS of thiophene and the decomposition of NH₃.     

Liquid phase methanol reforming with water over silica supported Pt–Ru catalysts

The mechanism of the liquid phase methanol reforming reaction over silica supported Pt–Ru catalyst was investigated by kinetic studies, employing a pyrex glass reactor with reflux condensers connected to a closed gas circulation system under ambient pressure. The rate of H₂ formation over Pt–Ru/SiO₂ catalysts was more than 20 times faster than that over Pt/SiO₂ catalysts with high selectivity for CO₂ (72.3%), indicating a marked addition effect of Ru. In the case of HCHO–H₂O reaction over Pt–Ru/SiO₂, the H₂ formation rate was five times larger than that in the CH₃OH–H₂O reaction but selectivity to CO₂ was only 4%. On the contrary, in the HCOOCH₃–H₂O and HCOOH–H₂O reactions, both high activity and selectivity were observed over Pt–Ru/SiO₂. These results clearly indicate that the CO₂ formation does not proceed via HCHO decomposition and following water gas shift reaction. We propose the following pathway for liquid phase methanol reforming reaction over Pt–Ru/SiO₂; a partly dehydrogenated methanol (CH₂OH^*) is the initial reaction intermediate, from which H₂ and CO₂ are formed through HCOOCH₃ and HCOOH as the successive reaction intermediates.     

Preparation of Ru metal nanoparticles in mesoporous materials: influence of sulfur on the hydrogenating activity

Hydrogenating catalysts were prepared by inserting Ru into the pores of mesoporous Al-MCM-41 materials by selective adsorption of [Ru(NH₃)₆]³⁺. Ru/support catalysts were obtained after reduction with H₂. The activities of these catalysts in hydrogenation reactions were compared to those of Ru/HY and Ru/SiO₂. The catalytic properties in the absence of sulfur were tested in benzene hydrogenation, and the intrinsic activities of all the catalysts (either supported on mesoporous materials or on zeolites) were identical. It was concluded from this result that the dispersion of the Ru metallic phase was similar for all these catalysts. These samples were tested in the tetralin hydrogenation in pure H₂ and in the presence of H₂S (330 ppm of H₂S in H₂). They were found to be much less active than the zeolite-supported catalysts in the presence of H₂S. It is proposed that the lower activity of the catalysts supported on mesoporous materials is either due to their milder acidity, as evidenced by NH₃-TPD, cumene cracking and pyridine desorption experiments, or to the localization of the Ru nanoparticles on alumina islands.     

Development of novel Ru catalyst of preferential CO oxidation for residential polymer electrolyte fuel cell systems

CO preferential oxidation on a novel Ru catalyst greatly improved in activity and selectivity over a wide temperature range by the pre-treatment of H₂ reduction was characterized. The high performance was obtained by increasing the population of surface Ru(0) which improved O₂ activation at low temperatures. Methanation of CO on the catalyst can also contribute to the final CO clean-up from ca. 100 to <1 ppm at low temperatures where the influence of CO₂ methanation can be ignored.     

Catalytic combustion of methane over supported bimetallic Pd catalysts: Effects of Ru or Rh addition

A series of Pd/γ-Al₂O₃ catalysts with various amounts of Ru or Rh with, and/or without, BaO were prepared by successive incipient wetness impregnation. The catalysts were investigated for the catalytic methane combustion before, and after, H₂S poisoning in an oxygen-rich atmosphere. The addition of ruthenium enhanced the catalytic activity for methane oxidation even after H₂S poisoning while maintaining the initial catalytic activity of the fresh catalyst. These results are explained in terms of dispersion of palladium by ruthenium and poisoning resistance of ruthenium. The addition of rhodium did not improve the overall activity in methane oxidation.     

Hydrogenation of tetralin on a sulfided ruthenium on KY zeolite catalyst. Effect of the sulfidation method

Hydrogenation of tetralin was used to modelize the hydrogenation of aromatic compounds in gasoils. This reaction was carried out under a 5 MPa hydrogen pressure, at 300°C, in the presence of hydrogen sulfide. Before reaction, the Ru on KY zeolite catalyst was presulfided in situ at 400°C either by a H₂S/H₂ mixture, or by dimethyl disulfide in n-heptane. The catalyst sulfided by dimethyl disulfide was 3 times less active than that sulfided by H₂S, due to coking during sulfidation. Another type of carbonaceous deposit was formed during the tetralin reaction, the nature and the amount of this deposit was not depending on the sulfidation method.     

Investigation of CoNiMo/Al2O3 catalysts: Relationship between H2S adsorption and HDS activity

Sulfidation of trimetallic CoNiMo/Al₂O₃ catalysts was studied by thermogravimetry at 400 °C under flow and pressure conditions. Results were compared with those obtained on prepared and industrial CoMo/Al₂O₃ and NiMo/Al₂O₃ catalysts. The amount of sorbed H₂S on the sulfided solids was measured at 300 °C in the H₂S pressure range 0–3.5 MPa at constant H₂ pressure (3.8 MPa). The adsorption isotherms were simulated using a model featuring dissociated adsorption of H₂S on supported metal sulfides and bare alumina. The amount of sulfur-vacancy sites could thus be determined under conditions close to industrial practice. A relationship with activity results for thiophene HDS and benzene hydrogenation was sought for.     

硫化氢对负载型钴铈双金属吸附剂脱除模拟煤气中单质汞的促进机理

采用共沉淀法制备了一系列不同配比的钴铈双金属吸附剂（Ce_xCo_yTi）,在固定床实验台上探究低温（80～240℃）下脱除模拟煤气中Hg⁰的特性及机理。结果表明,Ce、Co负载比为0.2、0.1时,在120℃、N₂+H₂S气氛下吸附剂表现出最佳的脱汞效果,其效率为95.3%;Ce_0.2Co_0.1Ti在N₂气氛下不仅存在物理吸附而且存在较强的化学吸附;在考察范围内,Ce_0.2Co_0.1Ti脱汞效率随H₂S浓度的增加而增加。采用基于DFT的第一性原理软件VASP模拟H₂S和Hg在Ce_0.2Co_0.1Ti表面的吸附及反应过程,表明Hg化学吸附于吸附剂表面,H₂S易解离形成S,且S极易与吸附态的Hg反应生成HgS,活化能垒为0.214eV,反应遵循Langmuir-Hinshelwood机理。     

H2S为毒物对乙炔氢氯化反应中AuCl3/AC催化剂催化活性的影响

采用等体积浸渍法制备了1% AuCl₃/AC催化剂,探究了硫化氢(H₂S)为毒物对乙炔氢氯化反应中催化剂催化活性的影响及失活机理。催化活性测试结果表明,以H₂S为毒物可导致乙炔氢氯化反应中的AuCl₃/AC催化剂的失活,且是一个不可逆过程;程序升温还原(TPR)和X射线光电子能谱(XPS)分析结果表明,H₂S的加入可有效地加快Au³⁺还原为Au⁰;透射电镜能谱(TEM-EDX)观测分析形成的Au-S化合物也可导致催化剂失活,即随着H₂S量的增大,更多的Au³⁺被还原为Au⁰,且形成的Au-S化合物覆盖在活性位点,使有效的活性组分降低进而导致AuCl₃/AC催化剂失活。     

Catalytic synthesis of methanethiol from hydrogen sulfide and carbon monoxide over vanadium-based catalysts

The direct synthesis of methanethiol, CH₃SH, from CO and H₂S was investigated using sulfided vanadium catalysts based on TiO₂ and Al₂O₃. These catalysts yield high activity and selectivity to methanethiol at an optimized temperature of 615 K. Carbonyl sulfide and hydrogen are predominant products below 615 K, whereas above this temperature methane becomes the preferred product. Methanethiol is formed by hydrogenation of COS, via surface thioformic acid and methylthiolate intermediates. Water produced in this reaction step is rapidly converted into CO₂ and H₂S by COS hydrolysis.

Titania was found to be a good catalyst for methanethiol formation. The effect of vanadium addition was to increase CO and H₂S conversion at the expense of methanethiol selectivity. High activities and selectivities to methanethiol were obtained using a sulfided vanadium catalyst supported on Al₂O₃. The TiO₂, V₂O₅/TiO₂ and V₂O₅/Al₂O₃ catalysts have been characterized by temperature programmed sulfidation (TPS). TPS profiles suggest a role of V₂O₅ in the sulfur exchange reactions taking place in the reaction network of H₂S and CO.     

Complete oxidation of methane at low temperature over Pt and Pd catalysts for the abatement of lean-burn natural gas fuelled vehicles emissions: influence of water and sulphur containing compounds

The catalytic activity of fresh Pd and Pt catalysts supported on γ-alumina in the complete oxidation of CH₄ traces under lean-burn conditions was studied in the presence or the absence of water or H₂S. Steam-aged catalysts were also studied in order to simulate long-term ageing in real lean-burn natural gas fuelled vehicles (NGVs) exhaust conditions. Without water or H₂S added to the feed, Pd catalysts exhibit a superior catalytic activity in methane oxidation compared to Pt ones, whatever the catalysts were fresh or aged. The addition of 10 vol.% water vapour to the feed strongly affects the activity of the fresh Pd catalyst, thus being only slightly more efficient than the fresh Pt one. H₂S has a strong poisoning effect on the catalytic activity of Pd catalysts, while Pt catalysts are more resistant. The fresh H₂S-poisoned Pd/Al₂O₃ catalyst was studied by TPD in O₂/He. Poisoning species decompose above 873 K as SO₂ and O₂ in relative concentrations consistent with the decomposition of surface sulphate species. However, a treatment in O₂/He at temperatures as high as 923 K does not allow the complete regeneration of the catalytic activity of H₂S-poisoned Pd/Al₂O₃. A mechanism involving the poisoning of PdO by sulphate species is proposed. Different diffusion processes by which these sulphate species can migrate back and forth between PdO and the support, depending on the experimental conditions, are suggested.     

Catalytic activities of Co(Ni)Mo/TiO2–Al2O3 catalysts in gasoil and thiophene HDS and pyridine HDN: effect of the TiO2–Al2O3 composition

The effect of the TiO₂–Al₂O₃ mixed oxide support composition on the hydrodesulfurization (HDS) of gasoil and the simultaneous HDS and hydrodenitrogenation (HDN) of gasoil+pyridine was studied over two series of CoMo and NiMo catalysts. The intrinsic activities for gasoil HDS and pyridine HDN were significantly increased by increasing the amount of TiO₂ into the support, and particularly over rich- and pure-TiO₂-based catalysts. It is suggested that the increase in activity be due to an improvement in reducing and sulfiding of molybdena over TiO₂. The inhibiting effect of pyridine on gasoil HDS was found to be similar for all the catalysts, i.e., was independent of the support composition. The ranking of the catalysts for the gasoil HDS test differed from that obtained for the thiophene test at different hydrogen pressures. In the case of gasoil HDS, the activity increases with TiO₂ content and large differences are observed between the catalysts supported on pure Al₂O₃ and pure TiO₂. In contrast, in the case of the thiophene test, the pure Al₂O₃-based catalyst appeared relatively more active than the catalysts supported on mixed oxides. Also, in the thiophene test the difference in intrinsic activity between the pure Al₂O₃-based catalyst appeared relatively more active than the catalysts supported on mixed oxides. Also in the thiophene test, the difference in intrinsic activity between the pure Al₂O₃- and pure TiO₂-based catalysts is relatively small and dependent on the H₂ pressure used. Such differences in activity trend among the gasoil and the thiophene tests are due to a different sensitivity of the catalysts (by different support or promoter) to the experimental conditions used. The results of the effect of the H₂ partial pressure on the thiophene HDS, and on the effect of H₂S concentration on gasoil HDS demonstrate the importance of these parameters, in addition to the nature of the reactant, to perform an adequate catalyst ranking.     

二氧化硅负载钌催化剂催化氨硼烷水解产氢研究

采用浸渍-还原法制备了Ru/SiO₂催化剂,并考察了钌负载量、还原剂硼氢化钠的用量、还原温度以及反应条件对催化剂Ru/SiO₂催化BH₃NH₃水解产氢的影响。结果表明,在钌的负载量为0.1%（质量分数）、还原剂硼氢化钠与钌的物质的量比为2.2∶1、还原温度为303 K时制备的催化剂,催化BH₃NH₃水解产氢速率最快[转化频率TOF为140.8 L H₂/（mol Ru·min）]。搅拌转速为450 r/min时,氨硼烷向催化剂表面传质最快,产氢速率最大。氨硼烷水解反应由催化剂界面反应控制,产氢速率与催化剂用量成正比。随着反应温度的升高,Ru活化的氨硼烷分子能量增加,反应速率逐渐增加。反应动力学计算表明Ru/SiO₂催化剂催化BH₃NH₃水解产氢反应对氨硼烷浓度为零级反应,活化能为45 kJ/mol。     

Development of an in-situ H2 reduction and moderate oxidation method for 3,5-dimethylpyridine hydrogenation in trickle bed reactor

The Ru/C catalyst prepared by impregnation method was used for hydrogenation of 3,5-dimethylpyridine in a trickle bed reactor. Under the same reduction conditions (300 °C in H₂), the catalytic activity of the non-in-situ reduced Ru/C-n catalyst was higher than that of the in-situ reduced Ru/C-y catalyst. Therefore, an in-situ H₂ reduction and moderate oxidation method was developed to increase the catalyst activity. Moreover, the influence of oxidation temperature on the developed method was investigated. The catalysts were characterized by Brunauer–Emmett–Teller method, hydrogen temperature programmed reduction H₂-TPR, hydrogen temperature-programmed dispersion (H₂-TPD), X-ray diffraction, energy dispersive spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, O₂ chemisorption and oxygen temperature-programmed dispersion (O₂-TPD) analyses. The results showed that there existed an optimal Ru/RuO_x ratio for the catalyst, and the highest 3,5-dimethylpyridine conversion was obtained for the Ru/C-i1 catalyst prepared by in-situ H₂ reduction and moderate oxidation (oxidized at 100 °C). Excessive oxidation (200 °C) resulted in a significant decrease in the Ru/RuO_x ratio of the in-situ H₂ reduction and moderate oxidized Ru/C-i2 catalyst, the interaction between RuO_x species and the support changed, and the hard-to-reduce RuO_x species was formed, leading to a significant decrease in catalyst activity. The developed in-situ H₂ reduction and moderate oxidation method eliminated the step of the non-in-situ reduction of catalyst outside the trickle bed reactor.     

Hydrocracking of diphenylmethaneRoles of H2S, pyrrhotite and pyrite

This study presents the role of H₂S other than H-transfer catalyst in the hydrocracking of diphenylmethane with H₂–H₂S-pyrrhotite. The results indicate that the partial pressure of H₂S controls the conversion of pyrrhotite to FeS and FeS₂, which in turn is closely related to the promotional activity of pyrrhotite on the diphenylmethane conversion. Under higher H₂S overpressures, pyrite bands appear in the Mössbauer spectra providing proof of the reversibility of pyrite decomposition under liquefaction conditions. With lower H₂S pressures, low activity troilite forms from the pyrrhotite. An enhanced activity was observed for a partial pressure of H₂S, sufficient for the maintenance of a high iron deficient surface on the pyrrhotite particles. When the partial pressure was increased too much, the formation of FeS₂ was observed with a slight decrease in activity. FeS did not show as great an activity as the non-stoichiometric pyrrhotite.     

Ru-Fe/Al_2O_3氧化-还原性能探究

以Al_2O_3为载体,RuCl_3·xH_2O和FeCl_3·6H_2O为活性组分前驱体,采用吸附-沉淀法制备了Ru-Fe/Al_2O_3和Ru/Al_2O_3催化剂,以马来酸二甲酯加氢合成丁二酸二甲酯为探针反应,结合H_2-TPR和XRD表征技术,考察Fe改性Ru基催化剂的氧化-还原性能及催化活性。经氧化-还原循环处理后,催化剂Ru-Fe/Al_2O_3上马来酸二甲酯加氢活性高于Ru/Al_2O_3。XRD结果显示,经处理的Ru-Fe/Al_2O_3上未见金属Ru的特征衍射峰,而Ru/Al_2O_3上出现了金属Ru的特征衍射峰。结合H_2-TPR结果推断,Ru与Fe之间发生了相互作用,这种协同作用可以改善Ru/Al_2O_3催化剂的热稳定性。     

Catalytic wet oxidation of H2S to sulfur on Fe/MgO catalyst

The room temperature wet catalytic oxidation was conducted in a batch reactor with Fe/MgO catalyst. Fe/MgO catalyst was prepared by the dissolution–precipitation method. XRD and temperature-programmed reductions (TPR) indicate that Fe oxide in the Fe/MgO is finely dispersed in the MgO support. The high H₂S removal capacities of Fe/MgO can be explained by the finely dispersed iron oxide MgO. The H₂S removal capacities of Fe/MgO are dependent on oxygen partial pressure (1.0 g H₂S/g_cat in air and 2.6 g H₂S/g_cat in oxygen). The valence state analysis of Fe/MgO catalyst suggests that the H₂S oxidation on Fe/MgO can occur by a redox couple reaction, reducing Fe³⁺ into Fe²⁺ by H₂S and oxidizing Fe²⁺ to Fe³⁺ by O₂.     

Oxidation of H2S on activated carbon KAU and influence of the surface state

Properties of the oxidized activated carbon KAU treated at different temperatures in inert atmosphere were studied by means of DTA, Boehm titration, XPS and AFM methods and their catalytic activity in H₂S oxidation by air was determined. XPS analysis has shown the existence of three types of oxygen species on carbon catalysts surface. The content of oxygen containing groups determined by Boehm titration is correlated with their amount obtained by XPS. Catalytic activity of the KAU catalysts in selective oxidation of hydrogen sulfide is connected with chemisorbed charged oxygen species (O_3.1 oxygen type with BE 536.8–537.7 eV) present on the carbons surface.

Formation of dense sulfur layer (islands of sulfur) on the carbons surface and removal of active oxygen species are the reason of the catalysts deactivation in H₂S selective oxidation. The treatment of deactivated catalyst in inert atmosphere at 300 °C gives full regeneration of the catalyst activity at low temperature reaction but only its partial reducing at high reaction temperature. The last case is connected with transformation of chemisorbed charged oxygen species into CO groups.

The KAU samples treated in flow of inert gas at 900–1000 °C were very active in H₂S oxidation to elemental sulfur transforming up to 51–57 mmol H₂S/g catalyst at 180 °C with formation of 1.7–1.9 g S_x/g catalyst.     

Hydrodeoxygenation of aliphatic esters on sulphided NiMo/γ-Al2O3 and CoMo/γ-Al2O3 catalyst: The effect of water

Water formed during hydrotreating of oxygen-containing feeds has been found to affect the performance of sulphided catalysts in different ways. The effect of water on the activity of sulphided NiMo/γ-Al₂O₃ and CoMo/γ-Al₂O₃ catalysts in hydrodeoxygenation (HDO) of aliphatic esters was investigated in a tubular reactor by varying the amount of water in the feed. In additional experiments, H₂S was added to the feed, alone and simultaneously with water.

Under the same conditions, the NiMo catalyst exhibited a higher activity than the CoMo catalyst. The ester conversions decreased with increase in the amount of added water. When H₂S and water were added simultaneously, the conversion increased to the same level as without water addition on the NiMo catalyst and reached a higher value on the CoMo catalyst. The conversions were highest, however, when only H₂S was added. Unfortunately, the conversions decreased with time under all conditions. On both catalysts, the total yield of the C₇ and C₆ hydrocarbons decreased with the amount of added water, while the concentrations of the oxygen-containing intermediates increased. The presence of H₂S improved the total hydrocarbon yield and shifted the main products towards the C₆ hydrocarbons. Thus, the addition of H₂S effectively compensated the inhibition by water.