共查询到20条相似文献,搜索用时 15 毫秒
1.
Tatsuya Takeguchi Shin-Nosuke Furukawa Masashi Inoue Koichi Eguchi 《Applied Catalysis A: General》2003,240(1-2):223-233
Ni catalysts supported on various solid solutions of ZrO2 with alkaline earth oxide and/or rare earth oxide were synthesized. The catalytic activities were compared for partial oxidation of methane and autothermal reforming of methane. For partial oxidation of methane, the Ni catalyst supported on a CaO–ZrO2 solid solution showed a high activity. Incorporation of CaO in the ZrO2 matrix was effective for increasing the reduction rate of the NiO particles and for decreasing the coke formation. On the other hand, the Ni particles supported on the CaO–CeO2–ZrO2 solid solution had a strong interaction with the support, and the Ni particles showed high activity and stability for autothermal reforming of methane. 相似文献
2.
Bettina Stolze Juliane Titus Stephan A. Schunk Andrian Milanov Ekkehard Schwab Roger Glä ser 《Frontiers of Chemical Science and Engineering》2016,10(2):281
Ni/SiO2-ZrO2 catalysts with Ni loadings of 1 to 13 wt-% were prepared, characterized by elemental analysis, X-ray diffraction, N2 sorption, temperature programmed oxidation, temperature programmed reduction, and tested for their activity and stability in the dry reforming of methane with carbon dioxide at 850 °C, gas hourly space velocity of 6000 and 1800 h–1 and atmospheric pressure. The SiO2-ZrO2 support as obtained through a simple and efficient sol-gel synthesis is highly porous (ABET = 90 m2·g–1, dP = 4.4 nm) with a homogeneously distributed Si-content of 3 wt-%. No loss of Si or formation of monoclinic ZrO2, even after steaming at 850 °C for 160 h, was detectable. The catalyst with 5 wt-% Ni loading in its fully reduced state is stable over 15?h on-stream in the dry reforming reaction. If the catalyst was not fully reduced, a reduction during the early stages of dry reforming is accompanied by the deposition of up to 44 mg·g–1carbon as shown by experiments in a magnetic suspension balance. Rapid coking occurs for increased residence times and times-on-stream starting at 50 h. The Ni loading of 5 wt-% on SiO2-ZrO2 was shown to provide an optimal balance between activity and coking tendency. 相似文献
3.
A. Topalidis D.E. Petrakis A. Ladavos L. Loukatzikou P.J. Pomonis 《Catalysis Today》2007,127(1-4):238-245
The kinetics of interconversion of methane with carbon dioxide was studied over a 0.5%Pt/SrTiO3 solid catalyst in the temperature range 813–893 K and partial pressure range 0.083<PCH4,PCO2<0.667. The fitting of the experimental data for the rate of methane conversion, RCH4, using the empirical equation RCH4=k1(PCH4)m(PCO2)n showed that both reaction orders n and m are steady and obtain values equal to m ≈ 1 and n ≈ 0. The results are explained using Langmuir–Hinshelwood kinetics with the reactants adsorbed on distinct and discreet active sites of the solids, namely the methane is weakly adsorbed on the metallic phase and the carbon dioxide is strongly adsorbed on the oxidic phase of the catalyst. The apparent activation energy for the reforming of methane was estimated to be 123 kJ mol−1.The rate of conversion of the carbon dioxide, RCO2, was also fitted using a similar empirical equation RCO2=k2(PCH4)m(PCO2)n. The results indicate that there is a positive but variable dependence on both reaction orders which increases in the temperature range 813–893 K from m ≈ 0.0 to m ≈ 0.30 and from n ≈ 0.3 to n ≈ 0.6. This variation is attributed to the variable participation of the rate of the reverse water gas shift reaction, Rrwgs, to the overall rate RCO2 of CO2 conversion. The dependence of Rrwgs on the partial pressure of CO2 appears similar to that of RCH4 on the same reactant but shows strong inhibition by the reaction products. The results are discussed using Langmuir–Hinshelwood kinetics with the reactants and products adsorbed competitively on similar active sites of the catalyst. 相似文献
4.
Nanocomposite Ni/ZrO2-AN catalyst consisting of comparably sized Ni metal and ZrO2 nanoparticles is studied in comparison with zirconia- and alumina-supported Ni catalysts (Ni/ZrO2-CP and commercial Ni/Al2O3-C) for steam reforming of methane (SRM) and for combined steam and CO2 reforming of methane (CSCRM). The reactions are performed under atmospheric pressure with stoichiometric amounts of H2O and CH4 or (H2O + CO2) and CH4 at 1073 K. Under a wide range of methane space velocity (gas hourly space velocity of methane GHSVCH4 = 12,000–96,000 ml/(h gcat.), the nanocomposite Ni/ZrO2-AN catalyst always shows higher activity and stability for both SRM and CSCRM reactions. The two supported Ni catalysts (Ni/ZrO2-CP and Ni/Al2O3-C) exhibit fairly stable catalysis under low GHSVCH4 but they are easily deactivated under high GHSVCH4 and become completely inactive when they are reacted for ca.100 h at GHSVCH4 = 48,000 ml/(h gcat.). The CSCRM reaction is carried out with different H2O/CO2 ratios in the reaction feed while keeping the molar ratio (H2O + CO2)/CH4 = 1.0, the results prove that the nanocomposite Ni/ZrO2-AN catalyst can be highly promising in enabling a catalytic technology for the production of syngas with flexible H2/CO ratios (ca. H2/CO = 1.0–3.0) to meet the requirements of various downstream chemical syntheses. 相似文献
5.
Keiichi Tomishige Osamu Yamazaki Yangguang Chen Kota Yokoyama Xiaohong Li Kaoru Fujimoto 《Catalysis Today》1998,45(1-4):35-39
Carbon deposition behavior in CO2 reforming of methane, methane decomposition, and CO disproportionation on nickel-magnesia solid solution was investigated by means of thermogravimetric analysis and temperature programmed reaction of deposited carbon with carbon dioxide. It was found that rapid oxidation of CHx on Ni surface by oxygen species from CO2 through dissociation at metal-support interface is a key step for the inhibition of carbon formation. 相似文献
6.
Dry reforming of methane has been investigated on two series of catalysts either prepared by co-precipitation: n(NixMgy)/Al, NixMgy and NixAly or prepared by impregnation: Ni/MgO (mol% Ni = 5, 10). The catalysts, calcined at 600–900 °C, were characterized by different techniques: BET, H2-TPR, TPO, XRD, IR, and TEM-EDX analysis. The surface BET (30–182 m2 g−1) decreased with increasing the temperature of calcination, after reduction and in the presence of Mg element. The XRD analysis showed, for n(NixMgy)/Al catalysts, the presence of NiAl2O4 and NiO–MgO solid solutions. The catalyst reducibility decreased with increasing the temperature of pretreatment. The n(NixMgy)/Al catalysts were active for dry reforming of methane with a good resistance to coke formation. The bimetallic catalyst Ni0.05Mg0.95 (calcined at 750 °C and tested at 800 °C) presents a poor activity. In contrast, the 5% Ni/MgO catalyst, having the same composition but prepared by impregnation, presents a high activity for the same calcination and reaction conditions. For all the catalysts the activity decreased with increasing the temperature of calcination and a previous H2-reduction of the catalyst improves the performances. The TPO profiles and TEM-EDX analysis showed mainly four types of coke: CHx species, surface carbon, nickel carbide and carbon nanotubes. 相似文献
7.
Jing Gao Zhaoyin Hou Jianzhong Guo Yinghong Zhu Xiaoming Zheng 《Catalysis Today》2008,131(1-4):278-284
In this contribution, a commercial spherical SiO2 was modified with different amounts of La2O3, and used as the support of Ni catalysts for autothermal reforming of methane in a fluidized-bed reactor. Nitrogen adsorption, XRD and H2-TPR analysis indicated that La2O3-modified SiO2 had higher surface area, strengthened interaction between Ni and support, and improved dispersion of Ni. CO2-TPD found that La2O3 increased the alkalescence of SiO2 and improved the activation of CO2. Coking reaction (via both temperature-programmed surface reaction of CH4 (CH4-TPSR) and pulse decomposition of CH4) disclosed that La2O3 reduced the dehydrogenation ability of Ni. CO2-TPO, O2-TPO (followed after CH4-TPSR) confirmed that only part amount of carbon species derived from methane decomposition could be removed by CO2, and O2 in feed played a crucial role for the gasification of the inactive surface carbons. Ni/xLa2O3-SiO2 (x = 10, 15, 30) possessed high activity and excellent stability for autothermal reforming of methane in a fluidized-bed reactor. 相似文献
8.
Jorge D.A. Bellido Eurico Y. Tanabe Elisabete M. Assaf 《Applied catalysis. B, Environmental》2009,90(3-4):485-488
Supported nickel catalysts of composition Ni/Y2O3–ZrO2 were synthesized in one step by the polymerization method and compared with a nickel catalyst prepared by wet impregnation. Stronger interactions were observed in the formed catalysts between NiO species and the oxygen vacancies of the Y2O3–ZrO2 in the catalysts made by polymerization, and these were attributed to less agglomeration of the NiO during the synthesis of the catalysts in one step. The dry reforming of ethanol was catalyzed with a maximum CO2 conversion of 61% on the 5NiYZ catalyst at 800 °C, representing a better response than for the catalyst of the same composition prepared by wet impregnation. 相似文献
9.
Ni catalysts supported on γ-Al2O3, CeO2 and CeO2–Al2O3 systems were tested for catalytic CO2 reforming of methane into synthesis gas. Ni/CeO2–Al2O3 catalysts showed much better catalytic performance than either CeO2- or γ-Al2O3-supported Ni catalysts. CeO2 as a support for Ni catalysts produced a strong metal–support interaction (SMSI), which reduced the catalytic activity and carbon deposition. However, CeO2 had positive effect on catalytic activity, stability, and carbon suppression when used as a promoter in Ni/γ-Al2O3 catalysts for this reaction. A weight loading of 1–5 wt% CeO2 was found to be the optimum. Ni catalysts with CeO2 promoters reduced the chemical interaction between nickel and support, resulting in an increase in reducibility and stronger dispersion of nickel. The stability and less coking on CeO2-promoted catalysts are attributed to the oxidative properties of CeO2. 相似文献
10.
Al2O3–SiO2 mixed oxide has been investigated as a support for hydrotreating catalyst with variation of its composition [Si/(Si + Al) = 0.06, 0.12, 0.31, 0.56, 0.78] and its interaction with the surface active metals (NiMo). The composition of support and surface species (NiMo) of catalysts were characterized by specific surface area, atomic absorption, SEM-EDX, XRD, temperature programmed reduction (TPR), Raman analysis, scanning electron microscopy (STEM) and transmission electron microscopy (TEM). Incorporation of SiO2 in Al2O3 promotes a weak interaction between the active phases and particularly catalyst that predominated with SiO2 content. The oxide and sulfided catalysts characterization indicated that the effect of support is responsible to form different catalytic sites. Crystallization of MoO3 phases and a relatively longer crystal of MoS2 in the sulfided catalyst were attributed to an increasing SiO2 content in the support. The catalytic behavior of the NiMo supported catalysts is explained in terms of structural changes on the surface due to the support and active metal interactions. The activity of the different catalysts evaluated in the thiophene hydrodesulfurization reaction was higher for the catalyst having lower SiO2 content in the support. 相似文献
11.
Bernd Steinhauer Mohan Reddy Kasireddy Jrg Radnik Andreas Martin 《Applied Catalysis A: General》2009,366(2):333-341
The present research deals with catalyst development for the utilization of CO2 in dry reforming of methane with the aim of reaching highest yield of the main product synthesis gas (CO, H2) at lowest possible temperatures. Therefore, Ni-Pd bimetallic supported catalysts were prepared by simple impregnation method using various carriers. The catalytic performance of the catalysts was investigated at 500, 600 and 700 °C under atmospheric pressure and a CH4 to CO2 feed ratio of 1. Fresh, spent and regenerated catalysts were characterized by N2 adsorption for BET surface area determination, XRD, ICP, XPS and TEM. The catalytic activity of the studied Ni-Pd catalysts depends strongly on the support used and decreases in the following ranking: ZrO2-La2O3, La2O3 > ZrO2 > SiO2 > Al2O3 > TiO2. The bimetallic catalysts were more active than catalysts containing Ni or Pd alone. A Ni to Pd ratio = 4 at a metal loading of 7.5 wt% revealed the best results. Higher loading lead to increased formation of coke; partly in shape of carbon nanotubes (CNT) as identified by TEM. Furthermore, the effect of different calcination temperatures was studied; 600 °C was found to be most favorable. No effect on the catalytic activity was observed if a fresh catalyst was pre-reduced in H2 prior to use or spent samples were regenerated by air treatment. Ni and Pd metal species are the active components under reaction conditions. Best conversions of CO2 of 78% and CH4 of 73% were obtained using a 7.5 wt% NiPd (80:20) ZrO2-La2O3 supported catalyst at a reaction temperature of 700 °C. CO and H2 yields of 57% and 59%, respectively, were obtained. 相似文献
12.
B. Pholjaroen N. Laosiripojana P. Praserthdam S. Assabumrungrat 《Journal of Industrial and Engineering Chemistry》2009,15(4):488-497
The carbon dioxide reforming of methane over commercial Ni/SiO2·MgO catalyst under periodic and steady state operations was investigated at a temperature range of 650–750 °C. Under steady state operation, methane conversions tended to be constant with reaction time but increased with increasing reaction temperature. It was then observed that at low temperature (650 °C) under the periodic operation, methane conversion was also constant at approximately 48% throughout reaction time, but for the operation at a higher temperature, i.e. 750 °C, higher methane conversion (about 67%) was initially achieved but decreased dramatically with reaction time (to 27% in 240 min). The reason for the catalyst deactivation particularly for the periodic operation was further investigated by TPO, BET and XRD. It is suggested that at different operating temperatures, various types of coke occurred on the surface of catalyst and affected the catalytic activity. 相似文献
13.
Aisling M. OConnor Yves Schuurman Julian R.H. Ross Claude Mirodatos 《Catalysis Today》2006,115(1-4):191-198
The mechanism of the CO2 reforming of methane reaction over the Pt/ZrO2 catalyst was investigated using a temporal analysis of products (TAP) reactor system. For comparative purposes, the reaction pathway using a Pt/Al2O3 catalyst was also examined. A reaction sequence is suggested for both catalysts. Over both catalysts, methane decomposition takes place over platinum. The main difference between the two catalysts concerns the carbon dioxide dissociation. Over Pt/Al2O3 this step is assisted by hydrogen. Over Pt/ZrO2 this step takes place over the zirconia support and involves surface vacancies. Moreover, large pools of formate and carbonate species are present on the zirconia. Transient studies conducted to determine the origin of carbon species accumulated during CO2 reforming revealed that more than 99% of the carbon was derived from the methane molecule over both catalysts. Over the Pt/ZrO2 catalyst, only a single very reactive carbon species was detected, while over the Pt/Al2O3 a second less active species was also formed. 相似文献
14.
Co–Nb2O5–SiO2 catalysts were prepared using three different sol–gel procedures: (i) the colloidal sol–gel method using NbCl5 and SiCl4 as precursors; (ii) the polymeric sol–gel method using niobium ethoxide and tetraethyl-orthosilicate (TEOS); (iii) an intermediate procedure between the colloidal and polymeric sol–gel method in which the precursors were those utilized in the CSG but dissolved in a mixture of anhydrous ethanol and CCl4. In all procedures, the elimination of the solvent carried out between 80 and 110°C was followed by a reduction in hydrogen flow (30 ml min−1) at 773 K. Following these procedures, samples containing 10 wt.% Co and 15 wt.% niobium oxide (expressed as Nb2O5) were obtained. The characterization of the catalysts was performed using various techniques: N2 adsorption and desorption curves at 77 K, NH3- and H2-chemisorption, TPO, XPS, XRD, and solid state 1H MAS-NMR. Hydrogenolysis of butane was evaluated. The low reaction rates are assigned to the effect of the metal size, whereas the isobutane selectivity as well as the relatively high stability is due to the acidity of the support. 相似文献
15.
The theoretical and experimental feasibility of direct conversion of CH4 and CO2 to acetic acid by an isothermal step-wise route over Pd/SiO2 and Rh/SiO2 catalysts was investigated. The methyl radical formation from CH4 dissociation and CO2 inserting into the intermediate are regarded as two limiting steps. Preliminary experimental results have shown that the following step-wise route can circumvent the thermodynamic limitation of this direct synthesis at low temperatures. Pd catalysts are more active than Rh catalysts at 170 °C and 200 °C, while formic acid is only produced on Pd catalysts. The optimum contact time of CH4 and CO2 with catalysts is 1 min under the experimental conditions. And there is no apparent deactivation resulting from carbon deposition for catalysts during the successive reaction cycles. 相似文献
16.
Koichi Yuzaki Takayoshi Yarimizu Kenji Aoyagi Shin-ichi Ito Kimio Kunimori 《Catalysis Today》1998,45(1-4):129-134
The study of catalytic decomposition of nitrous oxide to nitrogen and oxygen over Rh catalysts supported on various supports (USY, NaY, Al2O3, ZrO2, FSM-16, CeO2, La2O3) showed that the activities of Rh/Al2O3 and Rh/USY (ultrastable Y zeolite) catalysts were comparable to or higher than the other catalysts reported in the literatures. The catalytic activity of N2O decomposition was sensitive not only to the Rh dispersion but also to the preparation variables such as the Rh precursors and the supports used. A pulsed N2O experiment over a Rh/USY catalyst suggested that the catalytic N2O decomposition occurs on oxygen-covered surface and that O2 may be freed on collision of N2O molecules with the adsorbed oxygen atoms. 相似文献
17.
18.
The combined CO2 reforming and partial oxidation (POX) of n-heptane was studied on various noble metal zirconia catalysts between 700 and 900 °C. The activity order of the metals was Rh > Pd > Ir > Pt. Selectivity to syngas increased with the activity of the catalysts but the H2 to CO molar ratio decreased. The activity and selectivity of the 0.25 wt% Rh/ZrO2 catalyst were close to the performance of a commercial 15 wt% NiO/Al2O3 catalyst. The conversions and product compositions were compared to the calculated thermodynamic equilibria. 相似文献
19.
Caroline Cellier Donatienne Le Clef Ccilia Mateos-Pedrero Patricio Ruiz 《Catalysis Today》2005,106(1-4):47-51
The influence of the addition of 5 vol.% of carbon monoxide, hydrogen, carbon dioxide or water to the feed of partial oxidation of methane was investigated over Ni/γ-Al2O3 and Rh/γ-Al2O3 catalysts. In addition to catalytic tests, thermodynamic calculations were performed to predict the effect of these gas co-feeds. Compared to the thermodynamic trends, differences in the influence of the co-feeding on catalytic performances were observed between both catalysts. Co-feeding of CO, H2, CO2 or H2O can modify the oxidation state and dispersion of the metal component of the catalysts during reaction, and as a consequence, their performances. Changes in catalysts can be due to dynamic processes occurring during reaction. It is suggested to take these processes into account in a more complex kinetic equation for the reactions involved. 相似文献
20.
Stphanie Lambert Benoît Heinrichs Alain Brasseur Andr Rulmont Jean-Paul Pirard 《Applied Catalysis A: General》2004,270(1-2):201-208
The combination of results from carbon monoxide chemisorption, X-ray diffraction, and transmission electron microscopy allowed calculating the surface composition of the palladium–copper nanoparticles in Pd–Cu/SiO2 cogelled xerogel catalysts. Values obtained indicate a very pronounced surface enrichment with copper. Surface compositions obtained with this method, which combines three different experimental techniques, are in agreement with the literature data previously obtained for surface segregation in Pd–Cu/SiO2 catalysts by other techniques as low energy ion scattering and X-ray photoelectron spectroscopy. While 1,2-dichloroethane hydrodechlorination over pure palladium mainly produces ethane, increasing copper content in bimetallic catalysts results in an increase in ethylene selectivity, to reach 100% in ethylene selectivity for the sample containing 1.4 wt.% of palladium and 3.0 wt.% of copper. 相似文献