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1.
The interactions of H2 and H2S molecules with Pt–Pd bimetallic catalysts were investigated at the molecular level using a DFT (density functional theory) approach to better understand the structures and properties of active sites, and the relations between structural changes and sulfur resistance. It was found that when alloying the Pt catalyst with a small amount of Pd at a particular surface atomic ratio range, both H2 and H2S showed different adsorption properties compared to those on monometallic Pt or Pd catalyst. The adsorptions of both H2 and H2S were enhanced, but the adsorption energy of H2 increased more than that of H2S, indicating that the adsorption of H2S became less favorable compared with H2 on the bimetallic Pt–Pd catalyst surface. The desorption energy of hydrogen from monometallic Pt or Pd, as well as bimetallic Pt–Pd supported on zeolite, were calculated by temperature-programmed desorption (TPD), the values were compared against the DFT results to explain experimentally and theoretically why the bimetallic Pt–Pd catalyst has better sulfur resistance than monometallic Pt catalyst. 相似文献
2.
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. 相似文献
3.
The influence of H2S partial pressure over the catalytic activity of MoS2, supported on three different oxides: Al2O3, TiO2 and ZrO2, was studied in the hydrodesulfurization of dibenzothiophene (DBT). A complex inhibiting effect is observed and two orders of reaction relative to H2S were determined: −1/2 and 0, as a function of H2S partial pressure. The experimental results are in good agreement with the kinetic models whereby the DBT transformation takes place through a dihydrogenated intermediate (DH-DBT). The associated mechanism considers that the heterolytic dissociative adsorption of H2 and H2S occurs over an unsaturated Mo ion and over a stable sulfur ion. 相似文献
4.
Gradient-corrected density functional theory was used to investigate the adsorption of H2S on Pd(1 1 1) surface. Molecular adsorption was found to be stable with H2S binding preferentially at top sites. In addition, the adsorption of other S moieties (SH and S) was investigated. SH and S were found to be preferentially bind at the bridge and fcc sites, respectively. The reaction pathways and energy profiles for H2S decomposition giving rise to adsorbed S and H were determined. Both H2S(ad) → SH(ad) + H(ad) and SH(ad) → S(ad) + H(ad) reactions were found to have low barriers and high exothermicities. This reveals that the decomposition of H2S on Pd(1 1 1) surface is a facile process. 相似文献
5.
Keiichi Tomishige Tomohisa Miyazawa Takeo Kimura Kimio Kunimori Naoto Koizumi Muneyoshi Yamada 《Applied catalysis. B, Environmental》2005,60(3-4):299-307
In the partial oxidation of tar derived from the pyrolysis of cedar wood, the effect of H2S addition was investigated over non-catalyst, steam reforming Ni catalyst, and Rh/CeO2/SiO2 using a fluidized bed reactor. In the non-catalytic gasification, the product distribution was not influenced by the presence of H2S. Steam reforming Ni catalyst was effective for the tar removal without H2S addition, however, the addition of H2S deactivated drastically. In contrast, Rh/CeO2/SiO2 exhibited higher and more stable activity than the Ni catalyst even under the presence of high concentration of H2S (280 ppm). On the Ni catalyst, the adsorption of sulfur was observed by XPS and Ni species was oxidized during the partial oxidation of tar. In the case of Rh/CeO2/SiO2, the adsorption of sulfur was below the detection limit of XPS. This can be related to the self-cleaning of catalyst surface during the circulation in the fluidized bed reactor for the partial oxidation of tar derived from cedar pyrolysis. 相似文献
6.
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(CexCoyTi),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%;Ce0.2Co0.1Ti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,Ce0.2Co0.1Ti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Ce0.2Co0.1Ti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。 相似文献
7.
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. 相似文献
8.
To define the roles of H2S and pyrrhotite in high temperatures employed for normal coal liquefaction, diphenylmethane hydrocracking with H2 and H2-H2S was carried out with and without pyrrhotite. H2S promotes diphenylmethane hydrocracking with H2 both in the presence and absence of pyrrhotite, and the reaction is dependent upon the H2S pressure in both instances. It is also dependent on the H2 pressure when pyrrhotite is present. The results are interpreted in terms of H2S acting as a hydrogen transfer catalyst. 相似文献
9.
采用密度泛函理论方法研究H2S与NiFe2O4(001)完整表面和氧缺陷表面的相互作用机理。结果表明,H2S在NiFe2O4氧载体表面Ni原子位的吸附能比其在Fe原子位的吸附能大。氧缺陷的形成会使H2S在氧载体表面金属原子位的吸附能增大,并且Ni原子位吸附H2S的吸附能增加更为明显。因而,NiFe2O4氧载体表面的Ni原子位是H2S的主要吸附位。同时采用热力学方法进一步研究含H2S的合成气与NiFe2O4氧载体之间的反应,发现H2S与氧载体的反应产物与氧载体的还原程度密切相关。由于铁氧化物的深度还原过程受到热力学限制,H2S与NiFe2O4氧载体反应的主要产物为Ni3S2。密度泛函理论方法与热力学方法研究结果均表明H2S倾向于与NiFe2O4氧载体中Ni发生相互作用,这将对NiFe2O4氧载体的反应性能产生不利影响。 相似文献
10.
用共沉淀法制备了一系列Ce-Cu-Al-O复合金属氧化物吸附剂,用于低温下脱除CO2气体中的微量H2S。采用XRD、N2物理吸附、SEM及XPS等手段对脱硫前后的吸附剂结构进行表征。研究了Ce含量、煅烧温度、气体空速、杂质气体及吸附温度对吸附剂脱除H2S性能的影响。结果表明,Ce-Cu-Al-O系列吸附剂在40℃条件下可有效脱除CO2气体中的H2S,Ce含量为10%的吸附剂(10Ce-Cu-Al-O)具有最大H2S穿透吸附量,为94.1mg/g。研究发现,引入CeO2能有效改善CuO的分散性,提高吸附剂的比表面积和孔容。提高煅烧温度,较大空速均不利于吸附剂的脱硫效果;平衡气CO2会抑制H2S的吸附;吸附温度不高于100℃时,10Ce-Cu-Al-O的穿透吸附量随温度升高而增加且不会生成COS副产物。表征结果显示,硫化后吸附剂的组分团聚导致了比表面积和孔容降低。此外,失活后的脱硫剂可在100℃用空气再生。 相似文献
11.
We report results on the adsorption and desorption of H2S on polycrystalline UO2 at 100 and 300 K, using ultrahigh vacuum X-ray photoelectron spectroscopy (XPS), low energy ion scattering (LEIS), and temperature programmed desorption (TPD). Our work is motivated by the potential for using the large stockpiles of depleted uranium in industrial applications, e.g., in catalytic processes, such as hydrodesulfurization (HDS) of petroleum. H2S is found to adsorb molecularly at 100 K on the polycrystalline surface, and desorption of molecular H2S occurs at a peak temperature of 140 K in TPD. Adsorption rates of sulfur as a function of H2S exposure are measured using XPS at 100 K; the S 2p intensity and lineshapes demonstrate that the saturation coverage of S-containing species is 1 monolayer (ML) at 100 K, and is 0.3–0.4 ML of dissociation fragments at 300 K. LEIS measurements of adsorption rates agree with XPS measurements. Atomic S is found to be stable to >500 K on the oxide surface, and desorbs at 580 K. Evidence for a recombination reaction of dissociative S species is also observed. We suggest that O-vacancies, defects, and surface termination atoms in the oxide surface are of importance in the adsorption and decomposition of S-containing molecules. 相似文献
12.
Silicalite-1 zeolite composite membranes 总被引:2,自引:0,他引:2
This review paper discusses the preparation of silicalite-1 zeolite membranes, the experimental procedures used for gas separation measurements and the results of single gas and gas mixture experiments. Silicalite-alumina composite membranes were prepared by an in-situ zeolite synthesis method using an alumina membrane tube with a 5-nm-pore-diameter, γ-alumina layer as a substrate. Single gas permeances of H2, Ar, n-C4H10, i-C4H10 and SF6 were measured and mixtures of H2/i-C4H10 and H2/SF6 were separated to characterize the silicalite membrane. These measurements were made from 300 to 737 K. Transport through the silicalite membrane appeared to be controlled by molecular size and adsorption properties. Permeances of all components studied were activated, and activation energies ranged from 8.5 to 16.2 kJ/mol. The ratio of single gas permeances was as high as 136 for H2/SF6 and 1100 for H2/i-C4H10 at 298 K. Separation selectivities at elevated temperatures were significantly above Knudsen diffusion selectivity and were larger than ratios of pure gas permeances at the same temperature. The largest permeance ratio for the separation of mixtures was 12.8 for H2/SF6 at 583 K. Separation selectivities were higher when a pressure drop was maintained across the membrane than when an inert sweep gas was used because of counter diffusion of the sweep gas. 相似文献
13.
Shiguang Li John L. Falconer Richard D. Noble 《Microporous and mesoporous materials》2008,110(2-3):310-317
Silicoaluminophosphate (SAPO) membranes with Si/Al gel ratios from 0.05 to 0.3 were synthesized by in situ crystallization onto porous, tubular stainless steel support. Pure SAPO-34 membranes were obtained when the Si/Al ratio was 0.15 or higher. The adsorbate polarizability correlated with the adsorption capacity on SAPO-34, and the amounts of gases adsorbed were in the order: CO2 > CH4 > N2 > H2. The Si/Al ratio did not affect the pore volume significantly, but it changed the CO2 and CH4 adsorption equilibrium constants. The SAPO-34 membranes effectively separated CO2 from CH4 for feed pressures up to 7 MPa. At 295 K, for a pressure drop of 138 kPa and a 50/50 feed, the CO2/CH4 selectivity was 170 for a membrane with a Si/Al gel ratio of 0.15. At 7 MPa, the CO2/CH4 selectivity was 100 and the CO2 permeance was 4 × 10−8 mol/(m2 · s · Pa) at 295 K. This membrane was also separated CO2/N2 (selectivity = 21) and H2/CH4 (selectivity = 32) mixtures at 295 K and a pressure drop of 138 kPa. Competitive adsorption and difference in diffusivities are responsible for CO2/CH4 and CO2/N2 separations, whereas the H2/CH4 separation was due to diffusivity differences. For a membrane with Si/Al gel ratio of 0.1, a mixture of SAPO-34 and SAPO-5 formed, and the CO2/CH4 selectivity was lower. 相似文献
14.
15.
The simultaneous absorption of H2S and CO2 has been studied both experimentally and theoretically. A model has been developed which predicts the absorption rates of H2S and CO2 into a sodium carbonate solution. The absorption rates are calculated according to the two-film theory. In the liquid film, the finite rate of the CO2 reaction was considered. Otherwise, in the liquid film as well as in the liquid bulk, equilibrium conditions for all reactions were assumed. Absorption experiments were performed on a packed column using a counter-flow strategy. In the experiments the influence of the initial carbonate concentration, the gas flow rate and the temperature on the removal efficiencies of H2S and CO2 and the selectivity of H2S were investigated. It is desirable to absorb the H2S but not the CO2. The agreement between the absorption model and the experimental results from the absorber tower was satisfactory. The mass transfer coefficients were determined by fitting the experimental data to the model with respect to the H2S and CO2 content in the outgoing gas. The H2S content was used to determine the gas side mass transfer coefficient and the CO2 content was used to determine the liquid side mass transfer coefficient, The effective contact area of mass transfer was taken from published data. With a constant packing height, both the experiments and the model indicated that high carbonate concentration benefits the removal efficiency of H2S. Higher gas flow rate also benefits the selectivity for H2S. However, the removal efficiency will decrease. At higher temperatures the selectivity and the removal efficiency of H2S decreased. Under the conditions investigated, the absorption of H2S was essentially controlled by gas-side mass transfer and the absorption of CO2 was controlled by liquid-side mass transfer 相似文献
16.
ZEC(zero emission coal)系统中,粗煤气进入碳酸化/重整炉前需先脱除H2S,提出利用经过多次碳酸化/煅烧捕集CO2循环的煅烧石灰石(CaO)脱除H2S,并研究循环碳酸化/煅烧次数、硫化温度、H2S浓度和微观结构对循环CaO硫化特性的影响。结果表明,多次循环碳酸化/煅烧捕集CO2后CaO仍具有较高H2S吸收性能。前20次循环,CaO硫化转化率随循环次数增加迅速降低;20次循环后,CaO硫化转化率缓慢下降。硫化120 min后,未循环CaO的硫化转化率接近100%,而经历1、20和100次循环后CaO的硫化转化率分别为94%、81%和74%。H2S浓度对循环CaO硫化性能影响较大。硫化温度(800~1000℃)对循环CaO的硫化性能影响较小,最佳硫化温度为900℃。随循环次数增加,CaO颗粒发生高温烧结,导致比表面积降低和20~150 nm内孔隙减少,而这是与H2S吸收密切相关的孔隙,导致CaO硫化转化率降低。 相似文献
17.
将H2S和CO2混合酸气一步转化制合成气,既实现了二者无害化处理,又生产出合成气,是一条理想的废气资源化利用新路线。由于分子结构稳定,在常规条件下因受热力学平衡限制,二者转化率极低。而在低温等离子体中,H2S和CO2可被激发为高活性物种来参与反应。研究了具有不同Si/Al摩尔比的ZSM-5催化剂与低温等离子体结合实现H2S-CO2一步高选择性制合成气,显著提高了H2S-CO2转化性能。考察了ZSM-5催化剂中Si/Al比和低温等离子体放电条件等对反应的影响。其中,当Si/Al比为80时表现出最优催化性能,最高H2和CO产率分别达到56.1%和10.0%。对常规条件和低温等离子体氛围下的不同ZSM-5催化剂上CO2、H2S、CO、H2等化学吸脱附行为进行了对比研究,发现低温等离子体促进了催化剂对CO2、H2及CO分子的吸附活化,进而明显提升了H2S和CO2转化。 相似文献
18.
Cobalt sulphide catalyst prepared via a new method involving the precipitation reaction between cobaltous acetate and ammonium sulphide solutions has been shown to be favourably active for the catalytic decomposition of H2S when compared with data for other transition metal sulphides.
The BET surface area of this unsupported catalyst is about an order of magnitude higher than cobalt sulphide formed by direct sulphidation of cobalt oxide with H2S gas. XRD, SEM and TEM analyses were used to obtain bulk composition and morphological characteristics. Catalyst specimen calcined at 823 K showed the best activity.
The kinetics of the decomposition reaction has been studied over this new preparation. Experiments conducted at atmospheric pressure between 933-983 K using about 11 feed compositions showed that below 40% H2S/Ar the reaction was essentially 1st order with respect to H2S partial pressure. Beyond this point, rate remained invariant with feed composition. A mechanism involving catalysis via co-ordinative unsaturation sites on the CoS was proposed and kinetic model based on the cleavage of the surface H-S bond as the rate-determining step appeared to be the most adequate representation of the rate data. Hydrogen production rates at all temperatures also paralleled the behaviour seen for H2S decomposition. Activation energy for H2S decomposition and H2 production rates were estimated as 111 kJ mol-1 and 88 kJ mol-1 respectively 相似文献
The BET surface area of this unsupported catalyst is about an order of magnitude higher than cobalt sulphide formed by direct sulphidation of cobalt oxide with H2S gas. XRD, SEM and TEM analyses were used to obtain bulk composition and morphological characteristics. Catalyst specimen calcined at 823 K showed the best activity.
The kinetics of the decomposition reaction has been studied over this new preparation. Experiments conducted at atmospheric pressure between 933-983 K using about 11 feed compositions showed that below 40% H2S/Ar the reaction was essentially 1st order with respect to H2S partial pressure. Beyond this point, rate remained invariant with feed composition. A mechanism involving catalysis via co-ordinative unsaturation sites on the CoS was proposed and kinetic model based on the cleavage of the surface H-S bond as the rate-determining step appeared to be the most adequate representation of the rate data. Hydrogen production rates at all temperatures also paralleled the behaviour seen for H2S decomposition. Activation energy for H2S decomposition and H2 production rates were estimated as 111 kJ mol-1 and 88 kJ mol-1 respectively 相似文献
19.
A nickel-based catalytic filter material for the use in integrated high temperature removal of tars and particles from biomass gasification gas was tested in a broad range of parameters allowing the identification of the operational region of such a filter. Small-scale porous alumina filter discs, loaded with approximately 2.5 wt% Al2O3, 1.0 wt% Ni and 0.5 wt% MgO were tested with a particle free synthetic gasification gas with 50 vol% N2, 12 vol% CO, 10 vol% H2, 11 vol% CO2, 12 vol% H2O, 5 vol% CH4 and 0–200 ppm H2S, and the selected model tar compounds: naphthalene and benzene. At a typical face velocity of 2.5 cm/s, in the presence of H2S and at 900 °C, the conversion of naphthalene is almost complete and a 1000-fold reduction in tar content is obtained. Technically, it would be better to run the filter close to the exit temperature of the gasifier around 800–850 °C. At 850 °C, conversions of 99.0% could be achieved in typical conditions, but as expected, only 77% reduction in tars was achieved at 800 °C.
Conversion data can be reasonably well described with first order kinetics and a dominant adsorption inhibition of the Ni sites by H2S. The apparent activation energies obtained are similar to those reported by other investigators: 177 kJ/mol for benzene and 92 kJ/mol for naphthalene. The estimated heat of adsorption of H2S is 71 kJ/mol in the benzene experiments and 182 kJ/mol in the naphthalene experiments, which points at very strong adsorption of H2S. Good operation of the present material can hence only be guaranteed at temperatures above 830 °C mainly due to the strong deactivation by H2S at lower temperatures. 相似文献
20.
《Chemical Engineering and Processing: Process Intensification》2002,41(9):5773-792
Due to its toxic and corrosive nature, H2S should be safely removed from the gases produced in gasification or combustion processes. In this study, adsorption of hydrogen sulfide was investigated on a natural zeolite, namely clinoptilolite. H2S adsorption characteristics of Western Anatolian clinoptilolite was studied in a fixed-bed system at different temperatures between 100 and 600 °C at atmospheric pressure. H2S adsorption capacity of clinoptilolite was found to be about 0.03 g S/g clinoptilolite at 600 °C. A deactivation model considering concentration dependence of activity term was applied to experimental results and adsorption rate constant and activation energy values were evaluated. Good agreement of the experimental breakthrough curves with the model predictions was observed. 相似文献