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1.
Sulfidation of trimetallic CoNiMo/Al 2O 3 catalysts was studied by thermogravimetry at 400 °C under flow and pressure conditions. Results were compared with those obtained on prepared and industrial CoMo/Al 2O 3 and NiMo/Al 2O 3 catalysts. The amount of sorbed H 2S on the sulfided solids was measured at 300 °C in the H 2S pressure range 0–3.5 MPa at constant H 2 pressure (3.8 MPa). The adsorption isotherms were simulated using a model featuring dissociated adsorption of H 2S 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
2.
The selective catalytic reduction of NO by H 2 under strongly oxidizing conditions (H 2-SCR) in the low-temperature range of 100–200 °C has been studied over Pt supported on a series of metal oxides (e.g., La 2O 3, MgO, Y 2O 3, CaO, CeO 2, TiO 2, SiO 2 and MgO-CeO 2). The Pt/MgO and Pt/CeO 2 solids showed the best catalytic behavior with respect to N 2 yield and the widest temperature window of operation compared with the other single metal oxide-supported Pt solids. An optimum 50 wt% MgO-50wt% CeO 2 support composition and 0.3 wt% Pt loading (in the 0.1–2.0 wt% range) were found in terms of specific reaction rate of N 2 production (mols N 2/g cat s). High NO conversions (70–95%) and N 2 selectivities (80–85%) were also obtained in the 100–200 °C range at a GHSV of 80,000 h −1 with the lowest 0.1 wt% Pt loading and using a feed stream of 0.25 vol% NO, 1 vol% H 2, 5 vol% O 2 and He as balance gas. Addition of 5 vol% H 2O in the latter feed stream had a positive influence on the catalytic performance and practically no effect on the stability of the 0.1 wt% Pt/MgO-CeO 2 during 24 h on reaction stream. Moreover, the latter catalytic system exhibited a high stability in the presence of 25–40 ppm SO 2 in the feed stream following a given support pretreatment. N 2 selectivity values in the 80–85% range were obtained over the 0.1 wt% Pt/MgO-CeO 2 catalyst in the 100–200 °C range in the presence of water and SO 2 in the feed stream. The above-mentioned results led to the obtainment of patents for the commercial exploitation of Pt/MgO-CeO 2 catalyst towards a new NO x control technology in the low-temperature range of 100–200 °C using H 2 as reducing agent. Temperature-programmed desorption (TPD) of NO, and transient titration of the adsorbed surface intermediate NO x species with H 2 experiments, following reaction, have revealed important information towards the understanding of basic mechanistic issues of the present catalytic system (e.g., surface coverage, number and location of active NO x intermediate species, NO x spillover). 相似文献
3.
In the partial oxidation of tar derived from the pyrolysis of cedar wood, the effect of H 2S addition was investigated over non-catalyst, steam reforming Ni catalyst, and Rh/CeO 2/SiO 2 using a fluidized bed reactor. In the non-catalytic gasification, the product distribution was not influenced by the presence of H 2S. Steam reforming Ni catalyst was effective for the tar removal without H 2S addition, however, the addition of H 2S deactivated drastically. In contrast, Rh/CeO 2/SiO 2 exhibited higher and more stable activity than the Ni catalyst even under the presence of high concentration of H 2S (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/CeO 2/SiO 2, 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
4.
Due to its toxic and corrosive nature, H 2S 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. H 2S adsorption characteristics of Western Anatolian clinoptilolite was studied in a fixed-bed system at different temperatures between 100 and 600 °C at atmospheric pressure. H 2S 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
5.
The feasibility of using a cobalt-molybdenum (Co-Mo) sulfide catalyst that was prepared from a commercial Co-Mo oxide catalyst for the production of elemental sulfur from hydrogen sulfide (H 2S) and carbon dioxide (CO 2) in a packed bed catalytic reactor was studied. It was demonstrated that the desired sulfide catalyst could be prepared by first reducing, then sulphiding the corresponding oxide. The results showed that the prepared catalyst was capable of producing elemental sulfur from the thermal decomposition of H 2S in the presence of CO 2 over a temperature range of 465-700°C and at atmospheric pressure. A specific rate coefficient was calculated as well as the Arrhenius parameters for the non-equilibrated reaction. The H 2S decomposition reaction was found to be a second order reaction and have an activation energy of 114.4kJ/mol(27.3kcal/mol). 相似文献
6.
The efficacy of using ZnO as an absorber for the removal of H 2S from small fuel processor steam reformate streams was examined. At temperatures below 300 °C, H 2S can in principle be reduced to below 100 ppbv, required for safe operation of PEM fuel cells. The ZnO adsorbent performed predictably based on ZnO-H 2S-ZnS-H 2O equilibria with steam, hydrogen, and CO 2 in the feed. However, addition of CO even at levels as low as 1 vol% drastically lowered the sulfur removal capability of the ZnO. This is consistent with the formation of COS by the reaction H 2S + CO = H 2 + COS. ZnO is not an efficient absorber for COS. Indirect evidence is also provided for the formation of COS via the reaction CO 2 + H 2S = COS + H 2O, which can occur in special cases when CO 2 is present but neither H 2O nor CO is present in the feed. The potential for COS formation compromises the ability of ZnO to deliver very low sulfur concentration reformate. 相似文献
7.
As a contribution to the development of a process for catalytic upgrading of tarry fuel gases, e.g. coke-oven gas, the conversion of naphthalene, benzene and methane on a nickel catalyst in the presence of H 2 and H 2O was studied. The experiments were performed in a tubular flow reactor (total pressure: 1.6 bar; residence time with respect to the empty reactor: 0.3 s; temperature: 400-950°C; and particle diameter of catalyst: 1.5 mm). The kinetic data were obtained by systematic variation of the reaction conditions. At temperatures of more than 800°C, each hydrocarbon is cracked and converted with H2O to CO and H2. Soot formation does not occur at any temperature. In case of simultaneous conversion of all three hydrocarbons, competitive reactions have to be considered. The rate of chemical reaction on the catalyst is substantially decreased in the presence of H2S. Nevertheless, in a reactor of industrial scale, H2S has only slight influence. The catalyst would be applied with a particle diameter of 19 mm (experiments: 1.5 mm), and the overall reaction rate of hydrocarbon conversion is significantly affected by gas film diffusion. 相似文献
8.
ZrO 2–TiO 2 mixed oxide (30–70 mol/mol) was prepared by low-temperature sol–gel followed by solvo-thermal treatment (1 day) at various temperatures (40, 80, 120, 160 and 200 °C). Selected samples of the corresponding single oxides were also prepared. Materials characterization was carried out by N 2 physisorption, XRD, thermal analysis (TG-DTA) and UV–vis DRS, infra-red and Laser-Raman spectroscopies. Binary solids of enhanced pore volume and pore size diameter were obtained by increasing the post-treatment severity. Anatase TiO 2 micro-segregation was evidenced by Raman spectroscopy for the mixed oxide solvo-treated at the highest temperature. This solid also showed the highest crystallization temperature to ZrTiO 4 (702 °C). Mo impregnated (2.8 atom nm −2) on various mixed oxides was sulfided under H 2S/H 2 (400 °C, 1 h), the catalysts being tested in the dibenzothiophene hydrodesulfurization (HDS, T = 320 °C, P = 5.59 MPa). By increasing the severity of the solvo-treatment improved supports for MoS 2 phase were obtained. The HDS activity of the catalyst with carrier post-treated at 200 °C was 40% higher (in per total mass basis) than that of sulfided Mo supported on the binary oxide solvo-treated at 80 °C. The ZrO 2–TiO 2-supported catalysts showed higher selectivity to products from the hydrogenation route than their counterparts supported on either single oxide. 相似文献
9.
The catalytic effect of a heteropolyacid, H 4SiW 12O 40, on nitrobenzene (20 and 30 μM) oxidation in supercritical water was investigated. A capillary flow-through reactor was operated at varying temperatures ( T=400–500 °C; P=30.7 MPa) and H 4SiW 12O 40 concentrations (3.5–34.8 μM) in an attempt to establish global power-law rate expressions for homogenous H 4SiW 12O 40-catalyzed and uncatalyzed supercritical water oxidation. Oxidation pathways and reaction mechanisms were further examined via primary oxidation product identification and the addition of various hydroxyl radical scavengers (2-propanol, acetone, acetone-d 6, bromide and iodide) to the reaction medium. Under our experimental conditions, nitrobenzene degradation rates were significantly enhanced in the presence of H 4SiW 12O 40. The major differences in temperature dependence observed between catalyzed and uncatalyzed nitrobenzene oxidation kinetics strongly suggest that the reaction path of H 4SiW 12O 40-catalyzed supercritical water oxidation (average activation Ea=218 kJ/mol; k=0.015–0.806 s −1 energy for T=440–500 °C; Ea=134 kJ/mol for the temperature range T=470–490 °C) apparently differs from that of uncatalyzed supercritical water oxidation ( Ea=212 kJ/mol; k=0.37–6.6 μM s −1). Similar primary oxidation products (i.e. phenol and 2-, 3-, and 4-nitrophenol) were identified for both treatment systems. H 4SiW 12O 40-catalyzed homogenous nitrobenzene oxidation kinetics was not sensitive to the presence of OH√ scavengers. 相似文献
10.
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 H 2S 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 Sx/g catalyst. 相似文献
11.
The activity of NO x storage-reduction (NSR) catalysts is greatly reduced by sulfur poisoning, caused by the SO 2 present in the exhaust stream. Desorption of sulfur species from poisoned NSR catalysts occurs at temperatures in excess of 600 °C using reducing atmospheres and conventional heating. In this work, microwave (MW) heating has been used to promote desulfurization of poisoned NSR catalysts. The experiments were carried out by heating the catalyst with MW radiation and using hydrogen as the reducing gas. Desorption of H 2S at 200 °C was observed. Desorption at even lower temperatures (150 °C) was observed when water was introduced to the system. In the presence of water, sulfur species desorbed as both H 2S and SO 2. An overall reduction of sulfur species of about 60% was obtained. The use of MW heating proves to be an efficient way to achieve regeneration of poisoned NSR catalysts. 相似文献
12.
Preliminary results are given on thermal decomposition characteristics of a high volatile A bituminous coal from Eastern Canada using vacuum pyrolysis experiments (pressure 2–200 mm Hg) over the temperature range 322–1000 °C. The objectives of the study were to determine the optimum temperature range for the formation of coal tar and to study the influence of reaction temperature on the nature of the solid residues. Significant decomposition reactions start at 300–400 °C and the optimum temperature range for the production of coal tar was 450–600 °C. The major gaseous products H 2S, CO 2 and CH 4 are formed up to 600 °C. Above 600 °C the coal decomposes mainly into CO and H 2. The solid residues are characterized by volatile matter content, calorific values and elemental analysis. The volatile matter content decreases rapidly from 322 °C and stabilizes at reaction temperatures > 750 °C. The 15% VM level, a minimum requirement in coal combustion processes, was reached at 500 °C. The changes in calorific values do not show any significant trend up to 600 °C, but decrease markedly above 600 °C. From the preliminary results vacuum pyrolysis is regarded as an effective process in which valuable coal tar by-products can be obtained from coal prior to its combustion. 相似文献
13.
The influence of SO 2, H 2S and COS in low concentrations on the deactivation of Pt/Rh/BaO/Al 2O 3 NO x storage catalysts was investigated. Different samples of the catalyst were exposed to synthetic gas mixtures mimicking lean/rich engine cycling in a mixed lean application at 400 °C. The lean gas mixture contained 8 vol.% O 2, 500 vol-ppm C 3H 6 and 400 vol-ppm NO balanced to 100 vol.% with Ar. The rich excursions were performed by switching off the oxygen supply. Sulphur, 25 vol-ppm of either SO 2, H 2S or COS, was added to the gas flow either during the lean, the rich or both periods. This procedure aimed at investigating the influence of the exposure conditions and therefore the lean and rich periods were kept equally long (5 min). In addition, thermodynamical calculations for the prevailing conditions were performed. It was concluded that all sulphur compounds investigated, i.e. SO2, H2S and COS, had similar, negative impact on the NOx storage ability of the catalyst and that they all showed increased deactivation rates during rich exposure compared to lean. During lean exposure, all sulphur carriers showed similar behaviour, while H2S and COS caused severe loss of noble metal activity during rich exposure. 相似文献
14.
The effects of H 2O and NH 3 on the kinetics of the liquid phase hydrogenation of tetralin to decalin at 6.9 MPa and 330°C over commercial P---Ni---Mo/alumina catalysts in the presence of H 2S have been investigated. H 2O functioned as a mild kinetic inhibitor to an extent sensitive to the H 2S level. Quasi in situ XPS was used to investigate the catalyst structure after exposure to H 20/H 2S. 相似文献
15.
Partial oxidation of methane to synthesis gas was carried out using supported iridium–nickel bimetallic catalysts, in order to reduce loading levels of iridium and nickel, and to avoid carbon deposition on nickel-based catalysts by adding iridium. The performance of supported iridium–nickel bimetallic catalysts in synthesis gas formation depended strongly upon the support materials. La 2O 3 gave the best performance among the support materials tested. Ir(0.25 wt%)–Ni(0.5 wt%)/La 2O 3 afforded 36% conversion of methane (CH 4/O 2=5) to give CO and H 2 with the selectivities of above 90% at 800°C, and those at 600°C were 25.3% conversion of methane and CO and H 2 selectivities of about 80%, respectively. Reduced monometallic Ir(0.25 wt%)/La 2O 3 and Ni(0.5 wt%)/La 2O 3 catalysts did not produce synthesis gas at 600°C. A higher conversion of methane was obtained by synergistic effects. The product concentrations of CO, H 2, and CO 2, and CH 4 conversion were maintained in high values, even increasing the space velocity of feed gas over Ir–Ni/La 2O 3 catalyst, indicating that rapid reaction takes place. As a by-product, a small amount of carbon deposition was observed, but carbon formation decreased with increasing the space velocity. On the other hand, with reduced monometallic Ni(10 wt%)/La 2O 3 catalyst, yield of synthesis gas and carbon decreased with increasing the space velocity. 相似文献
16.
Gradient-corrected density functional theory was used to investigate the adsorption of H 2S on Pd(1 1 1) surface. Molecular adsorption was found to be stable with H 2S 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 H 2S decomposition giving rise to adsorbed S and H were determined. Both H 2S (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 H 2S on Pd(1 1 1) surface is a facile process. 相似文献
17.
The relative-volume activities (RVAs) for real feedstocks HDS of four commercial CoMo/Al 2O 3 catalysts have been compared to the rates for thiophene and dibenzothiophene conversion. The reaction of thiophene competing with H 2S was studied in flow microreactors under a wide range of conditions: 300–400°C, overall pressure 0.1 or 3 MPa, thiophene pressure 8–125 kPa, H 2S content 0–15 mol%. The reaction of dibenzothiophene (DBT, 2 wt% in decaline) was carried out in a batch reactor at 335°C and 4 MPa. The conversion of the two model molecules proceeds through the same mechanism with a preliminary dearomatization step followed by parallel hydrogenolysis and hydrogenation. From kinetic modeling, the global rates and the contribution of the hydrogenation and hydrogenolysis routes to HDS were determined. Under pressure, hydrogenolysis was predominant. In that case, thiophene and DBT behaved similarly and their initial relative rates did not correlate the RVA. Industrial HDS is controlled by hydrogenation as evidenced by the good correlation between RVA and the rates of dearomatization of thiophene at atmospheric pressure and hydrogenation of the product biphenyl from DBT under pressure. It is concluded that the reaction of model molecules under selected conditions can appraise rapidly industrial HDS. 相似文献
18.
Catalytic desulphurization of benzothiophene (BTH) in a water/toluene emulsion, a model system for heavy oil emulsions, was achieved at 340°C using a water-soluble phosphomolybdic acid (PMA), a precursor for dispersed Mo catalyst. This process is based on the activation of H 2O to generate H 2 in situ via the water gas shift reaction (WGSR) for hydrodesulphurization (HDS). At 340°C with an initial CO loading of 4.14 MPa, essentially complete sulphur removal was obtained. Kinetic expressions for the WGSR and HDS of BTH with in situ generated H 2 and externally supplied H 2 were developed and verified experimentally. The kinetic analysis indicates that WGSR is rate-determining and desulphurization with in situ generated H 2 is a relatively fast step. Apparently, in situ H 2 is about seven times more active than externally supplied H 2 for the hydrogenation of BTH. A mechanism for desulphurization involving initial hydrogenation of BTH to dihydrobenzothiophene (DHBTH) followed by hydrogenolysis to give ethylbenzene (EB) and H 2S is proposed. 相似文献
19.
The sulphur tolerance and thermal stability of a 2 wt% Ag/γ-Al 2O 3 catalyst was investigated for the H 2-promoted SCR of NO x with octane and toluene. The aged catalyst was characterised by XRD and EXAFS analysis. It was found that the effect of ageing was a function of the gas mix and temperature of ageing. At high temperatures (800 °C) the catalyst deactivated regardless of the reaction mix. EXAFS analysis showed that this was associated with the Ag particles on the surface of the catalyst becoming more ordered. At 600 and 700 °C, the deactivating effect of ageing was much less pronounced for the catalyst in the H 2-promoted octane-SCR reaction and ageing at 600 °C resulted in an enhancement in activity for the reaction in the absence of H 2. For the toluene + H 2-SCR reaction the catalyst deactivated at each ageing temperature. The effect of addition of low levels of sulphur (1 ppm SO 2) to the feed was very much dependent on the reaction temperature. There was little deactivation of the catalyst at low temperatures (≤235 °C), severe deactivation at intermediate temperatures (305 and 400 °C) and activation of the catalyst at high temperatures (>500 °C). The results can be explained by the activity of the catalyst for the oxidation of SO 2 to SO 3 and the relative stability of silver and aluminium sulphates. The catalyst could be almost fully regenerated by a combination of heating and the presence of hydrogen in the regeneration mix. The catalyst could not be regenerated in the absence of hydrogen. 相似文献
20.
Zn–Ti-based sorbents promoted with cobalt and nickel additive were prepared by simple physical mixing of single oxides. Their capacities for removing H 2S and NH 3 simultaneously, emitted from coal gasifiers, were investigated in a micro-reactor at 1 atm and 650 °C. NH 3 within the fuel gases did not affect the sulfur removing capacity of the Zn–Ti-based sorbent. The additives, cobalt and nickel, were found to be active components in NH 3 decomposition as well as H 2S absorption, while major components such as ZnO and TiO 2 did not show any activity in the NH 3 decomposition reaction. NH 3 was decomposed over both oxide and sulfide forms of the additives, even though the NH 3 decomposition ability of their sulfides dramatically decreased in the presence of H 2 gas owing to the equilibrium limitation of NH 3 decomposition. In the case of oxide forms, cobalt oxide showed excellent NH 3 decomposition capacity regardless of H 2 concentrations, while the capacity of nickel oxide depended on the H 2 concentrations. 相似文献
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