Mechanistic study of partial oxidation of methane to synthesis gas over supported rhodium and ruthenium catalysts using in situ time-resolved FTIR spectroscopy

In situ time-resolved FTIR spectroscopy was used to study the reaction mechanism of partial oxidation of methane to synthesis gas and the interaction of CH₄/O₂/He (2/1/45) gas mixture with adsorbed CO species over SiO₂ and γ-Al₂O₃ supported Rh and Ru catalysts at 500–600°C. It was found that CO is the primary product for the reaction of CH₄/O₂/He (2/1/45) gas mixture over H₂ reduced and working state Rh/SiO₂ catalyst. Direct oxidation of methane is the main pathway of synthesis gas formation over Rh/SiO₂ catalyst. CO₂ is the primary product for the reaction of CH₄/O₂/He (2/1/45) gas mixture over Ru/γ-Al₂O₃ and Ru/SiO₂ catalysts. The dominant reaction pathway of CO formation over Ru/γ-Al₂O₃ and Ru/SiO₂ catalysts is via the reforming reactions of CH₄ with CO₂ and H₂O. The effect of space velocity on the partial oxidation of methane over SiO₂ and γ-Al₂O₃ supported Rh and Ru catalysts is consistent with the above mechanisms. It is also found that consecutive oxidation of surface CO species is an important pathway of CO₂ formation during the partial oxidation of methane to synthesis gas over Rh/SiO₂ and Ru/γ-Al₂O₃ catalysts.     

Catalytic conversion of methane and CO2 to synthesis gas over a La2O3-modified SiO2 supported Ni catalyst in fluidized-bed reactor

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.     

Reaction and oxygen permeation studies in Sm0.4Ba0.6Fe0.8Co0.2O3 − δ membrane reactor for partial oxidation of methane to syngas

A disk-type Sm_0.4Ba_0.6Co_0.2Fe_0.8O_3 − δ perovskite-type mixed-conducting membrane was applied to a membrane reactor for the partial oxidation of methane to syngas (CO + H₂). The reaction was carried out using Rh (1 wt%)/MgO catalyst by feeding CH₄ diluted with Ar. While CH₄ conversion increased and CO selectivity slightly decreased with increasing temperature, a high level of CH₄ conversion (90%) and a high selectivity to CO (98%) were observed at 1173 K. The oxygen flux was increased under the conditions for the catalytic partial oxidation of CH₄ compared with that measured when Ar was fed to the permeation side. We investigated the reaction pathways in the membrane reactor using different membrane reactor configurations and different kinds of gas. In the membrane reactor without the catalyst, the oxygen flux was not improved even when CH₄ was fed to the permeation side, whereas the oxygen flux was enhanced when CO or H₂ was fed. It is implied that the oxidation of CO and H₂ with the surface oxygen on the permeation side improves the oxygen flux through the membrane, and that CO₂ and H₂O react with CH₄ by reforming reactions to form syngas.     

Mechanistic evidence of the partial oxidation of methane to formaldehdye over silica based oxide catalysts by temperature programmed reaction studies

The catalytic behaviour of SiO₂ supported MoO₂ and V₂O₅ catalysts in the partial oxidation of methane to formaldehyde with O₂ (MPO) in the range 400–800°C has been investigated by temperature programmed reaction (TPR) tests. Both the sequence of the onset temperature of product formation and the product distribution patterns signal that MPO on silica based oxide catalysts occurs mainly via a consecutive reaction path: CH₄ → HCHO → CO → CO₂. At T >/ 700°C a parallel surface assisted gas-phase reaction pathway leads to the formation of minor amounts of C₂ products both on SiO₂ and MoO₃/SiO₂ catalysts. The redox properties of MoO₃/SiO₂ and V₂O₅SiO₂ catalysts have been systematically evaluated by H₂ and CH₄ temperature programmed reduction (H₂-TPR, CH₄-TPR) measurements. H₂-TPR results do not account for the reactivity scale of oxide catalysts in the MPO. CH₄-TPR measurements indicate that the enhancement in the specific activity of the silica is controlled by the capability of MoO₃ and V₂O₅ promoters in providing ‘active’ lattice oxygen species.     

The selective catalytic reduction of nitrogen oxides by methane on noble metal-loaded sulfated zirconia

The selective catalytic reduction of NO_x by methane on noble metal-loaded sulfated zirconia (SZ) catalysts was studied. Ru, Rh, Pd, Ag, Ir, Pt, and Au-loaded sulfated zirconia catalysts were compared with the intact sulfated zirconia. For the NO–CH₄–O₂ reaction, Ru, Rh, Pd, Ir, and Pt showed promotion effect on NO_x reduction, while for the NO₂–CH₄–O₂ reaction, only Rh and Pd showed promotion effect. Over intact and Rh, Pd, Ag, and Au-loaded sulfated zirconia, NO_x conversion in NO₂–CH₄–O₂ reaction was significantly higher than that in NO–CH₄–O₂ reaction, while clear difference was not observed over Ru, Ir, and Pt-loaded sulfated zirconia. Comparison of [NO₂]/([NO]+[NO₂]) in the effluent gases in NO–O₂ and NO₂–O₂ reactions showed that Ru, Ir, and Pt has high activity for NO oxidation under the reaction conditions. These facts suggest that effects of these metals toward NO_x reduction by methane can be categorized into the following three groups: (i) low activity for NO oxidation to NO₂, and high activity for NO₂ reduction to N₂ (Pd, Rh); (ii) high activity for NO oxidation to NO₂, and low activity for NO₂ reduction to N₂ (Ru, Ir, Pt); (iii) low activity for both reactions (Ag, Au). To confirm these suggestions, combination of these metals were investigated on binary or physically-mixed catalysts. The combination of Pd or Rh with Pt or Ru gave high activity for the selective reduction of NO_x by methane.     

Syngas conversion using RhVO4 and Rh2MnO4 catalysts: Regeneration and redispersion of Rh metal by calcination and reduction treatments

The hydrogenation of CO over mixed oxides (RhVO₄, Rh₂MnO₄) supported on SiO₂ has been studied after H₂ reduction at 300°C and at 500°C, and the results compared with those of unpromoted Rh/SiO₂ catalysts. Rh was more highly dispersed (40 Å) after the decomposition of RhVO₄ by the H₂ reduction than those of Rh₂MnO₄/SiO₂ and unpromoted Rh/SiO₂ catalysts. The activity and the selectivity to C₂ oxygenates of the mixed-oxide catalysts after the H₂ reduction were higher than those of the unpromoted Rh/SiO₂ catalysts, but the activity of the RhVO₄/SiO₂ catalyst increased more dramatically after the decomposition by the H₂ reduction at 300°C, and hence the yield of C₂ oxygenates increased. These results suggest that a strong metal–oxide interaction (SMOI) was induced by the decomposition of the mixed oxides after the H₂ reduction. The catalytic activity and selectivity were reproduced repeatedly by the calcination and reduction treatments of the spent (used) catalyst because of the regeneration of RhVO₄ and redispersion of Rh metal.     

静电纺丝法制备高活性多孔Ni/SiO2甲烷化催化剂

以三嵌段共聚物P123为模板剂,采用静电纺丝法制备了多孔Ni/SiO₂催化剂,考察其在CO甲烷化中的催化性能。采用N₂物理吸脱附测试、扫描电子显微镜（SEM）、X射线衍射（XRD）、H₂-程序升温还原（H₂-TPR）、透射电子显微镜（TEM）、热重分析（TGA）对催化剂的结构性质进行表征。结果表明,静电纺丝法制备的多孔Ni/SiO₂催化剂活性组分Ni在SiO₂载体纤维上高度分散,比表面积大,Ni颗粒尺寸小,金属与载体相互作用强,在CO甲烷化反应中表现出优异的催化活性和稳定性。在温度450℃,压力0.1 MPa,质量空速15000 ml/（g·h）条件下,多孔Ni/SiO₂催化剂CO转化率最高可达96.4%,CH₄选择性可达86.4%。此方法为工业上制备高催化活性且无须二次成型的甲烷化催化剂提供了新思路。     

Non-oxidative reaction of CBrF3 with methane over NiZSM-5 and HZSM-5

Catalytic hydrodehalogenation of CBrF₃ with methane was studied over NiZSM-5 and HZSM-5 in tubular reactor between 573 and 873 K and at ambient pressure. It was found that the incorporation of nickel into HZSM-5 significantly enhanced the activity of the zeolite. A variety of products were formed during reaction, including CH₃Br, CHF₃, CH₂Br₂, C₂F₆, C₂H₄, C₂H₂, C₂H₂F₂, CHBrF₂, CH₂BrF, and C₂H₃Br. XRD analysis showed that these two zeolite catalysts did not suffer any loss in their crystallinity during use. Deactivation of both NiZSM-5 and HZSM-5 may, in part, be due to poisoning of the zeolite by halogens. Coking is another cause of the deactivation of HZSM-5, but appears to play a minor role in NiZSM-5 deactivation. A series of methylated silicone oils was detected during reaction over NiZSM-5.     

CO hydrogenation over a rhodium vanadate catalyst: Reduction and regeneration of RhVO4 on SiO2

The hydrogenation of CO over an Rh vanadate (RhVO₄) catalyst supported on SiO₂ (RhVO₄/SiO₂) has been investigated after H₂ reduction at 500°C, and the results are compared with those of vanadia-promoted (V₂O₅–Rh/SiO₂) and unpromoted Rh/SiO₂ catalysts. The mean size of Rh particles, which were dispersed by the decomposition of RhVO₄ after the H₂ reduction, was smaller (41 Å) than those (91–101 Å) of V₂O₅–Rh/SiO₂ and Rh/SiO₂ catalysts. The RhVO₄/SiO₂ catalyst showed higher activity and selectivity to C₂ oxygenates than the unpromoted Rh/SiO₂ catalyst after the H₂ pretreatment. The CO conversion of the RhVO₄/SiO₂ catalyst was much higher than that of V₂O₅–Rh/SiO₂ catalyst, and the yield of C₂ oxygenates increased. We also found that the RhVO₄/SiO₂ catalyst can be regenerated by calcination or O₂ treatment at high temperature after the reaction.     

CH_4/N_2 separation on methane molecules grade diameter channel molecular sieves with a CHA-type structure

Samples of methane molecules grade diameter channel CHA-type molecular sieves(Chabazite-K, SAPO-34 and SSZ-13) were investigated using the adsorption separation of CH_4/N_2 mixtures. The isotherms recorded for CH_4 and N_2 follow a typical type-Ι behavior, which were fitted well with the Sips model(R~20.999) and the selectivity was calculated using IAST theory. The results reveal that Chabazite-K has the highest selectivity(SCH_4/N= 5.5).2 SSZ-13 has the largest capacity, which can adsorb up to a maximum of 30.957 cm~3·g~(-1)(STP) of CH_4, due to it having the largest pore volume and surface area, but the lowest selectivity(S_(CH_4/N_2)= 2.5). From the breakthrough test, we can conclude that SSZ-13 may be a suitable candidate for the recovery of CH_4 from low concentration methane(CH_420%) based on its larger pore volume and higher CH_4 capacity. Chabazite-K is more suited to the separation of high concentration methane(CH_450%) due to its higher selectivity.     

Low-temperature dry reforming of methane tuned by chemical speciations of active sites on the SiO2 and γ-Al2O3 supported Ni and Ni-Ce catalysts

The cognition of active sites in the Ni-based catalysts plays a vital role and remains a huge challenge in improving catalytic performance of low temperature CO₂ dry reforming of methane (LTDRM). In this work, typical catalysts of SiO₂ and γ-Al₂O₃ supported Ni and Ni-Ce were designed and prepared. Importantly, the difference in the chemical speciations of active sites on the Ni-based catalysts is revealed by advanced characterizations and further estimates respective catalytic performance for LTDRM. Results show that larger[Ni_n⁰] particles mixed with [Ni-O-Si_n]) species on the Ni/SiO₂(R) make CH₄ excessive decomposition, leading to poor activity and stability. Once the Ce species is doped, however, superior activity (59.0% CH₄ and 59.8% CO₂ conversions), stability and high H₂/CO ratio (0.96) at 600?℃ can be achieved on the Ni-Ce/SiO₂(R), in comparison with other catalysts and even reported studies. The improved performance can be ascribed to the formation of integral ([Ni_n⁰]-[Ce^III-□-Ce^III]) species on the Ni-Ce/SiO₂(R) catalyst, containing highly dispersed [Ni_n⁰] particles and rich oxygen vacancies, which can synergistically establish a new stable balance between gasification of carbon species and CO₂ dissociation. With respect to Ni-Ce/γ-Al₂O₃(R), the Ni and Ce precursors are easily captured by extra-framework Aln-OH groups and further form stable isolated ([Ni_n⁰]-[Ni-O-Al_n]) and [Ce^III-O-Al_n] species. In such a case, both of them preferentially accelerate CO₂ adsorption and dissociation, causing more carbon deposition due to the disproportionation of superfluous CO product. This deep distinguishment of chemical speciations of active sites can guide us to further develop new efficient Ni-based catalysts for LTDRM in the future.     

Fuel-rich catalytic combustion of methane in zero emissions power generation processes

A novel catalytic combustion concept for zero emissions power generation has been investigated. Catalysts consisting of Rh supported on ZrO₂, Ce-ZrO₂ or -Al₂O₃ were prepared and tested under fuel-rich conditions, i.e. for catalytic partial oxidation (CPO) of methane. The experiments were performed in a subscale gas-turbine reactor operating at 5 bar with exhaust gas-diluted feed mixtures.

The catalyst support material was found to influence the light-off temperature significantly, which increased in the following order Rh/Ce-ZrO₂ < Rh/ZrO₂ < Rh/-Al₂O₃. The Rh loading, however, only had a minor influence. The high activity of Rh/Ce-ZrO₂ is probably related to the high dispersion of Rh on Ce-ZrO₂ and the high oxygen mobility of this support compared to pure ZrO₂. The formation of hydrogen was also found to increase over the catalyst containing ceria in the support material.     

Fischer–Tropsch synthesis over Re-promoted Co supported on Al2O3, SiO2 and TiO2: Effect of water

The activity and selectivity of rhenium promoted cobalt Fischer–Tropsch catalysts supported on Al₂O₃, TiO₂ and SiO₂ have been studied in a fixed-bed reactor at 483 K and 20 bar. Exposure of the catalysts to water added to the feed deactivates the Al₂O₃ supported catalyst, while the activity of the TiO₂ and SiO₂ supported catalysts increased. However, at high concentrations of water both the SiO₂ and TiO₂ supported catalyst deactivated. Common for all catalysts was an increase in C₅₊ selectivity and a decrease in the CH₄ selectivity by increasing the water partial pressure. The catalysts have been characterized by scanning transmission electron microscope (STEM), BET, H₂ chemisorption and X-ray diffraction (XRD).     

氢气高温还原制备的负载型镍基催化剂用于苯酚加氢的性能

通过等体积浸渍法分别将Ni(NO₃)₂、NiCl₂、NiSO₄ 3种镍前体浸渍于A1₂O₃或SiO₂载体上,然后通过H₂高温还原法制备了负载型镍基催化剂,考察了镍前体、载体种类、镍负载量、反应条件等对镍基催化剂苯酚加氢性能的影响。结果表明,对比3种镍前体,在H₂高温还原体系中Ni(NO₃)₂最容易被还原,制备的镍基催化剂苯酚加氢活性最高。SiO₂负载的镍基催化剂活性远高于γ-Al₂O₃催化剂。适宜的Ni负载量有助于活性组分的分散和催化活性的提高。镍基催化剂的苯酚加氢产物以环己醇为主,相对缓和的反应条件更容易生成环己酮。在非极性溶剂正庚烷或环己烷存在下,苯酚加氢反应速率远远高于极性溶剂水或乙醇存在下的结果,而且环己酮的选择性更高。     

载体对Li-Mn氧化物催化甲烷氧化偶联反应作用

采用浸渍法制备不同金属氧化物载体负载的Li-Mn/MO_x(M=Mg,La,Ti,Si,Zr,Ta)催化剂,对其甲烷氧化偶联反应活性进行评价。结果表明,以TiO_2为载体制备的Li-Mn/TiO_2催化剂具有较高的CH_4转化率和C2烃选择性,C_2烃产率显著提高,金属氧化物TiO_2是Li-Mn复合氧化物的优良催化剂载体。n(Li)∶n(Mn)=1.0∶2.0形成的Li-Mn/TiO_2催化剂具有最高的CH_4转化率和C_2烃选择性,n(C_2H_4)∶n(C_2H_6)的增加有助于提高反应产物中C_2H_4的相对浓度,W元素的添加未能进一步提高Li-Mn/TiO_2催化剂的催化活性。Li-Mn/TiO_2催化剂在n(Li)∶n(Mn)=1.0∶2.0、反应温度775℃、反应压力0.1 MPa、V(CH_4)∶V(O_2)=2.5、空速7 200 m L·(h·g)~(-1)和催化剂用量0.5 g条件下,CH_4转化率达31.9%,C_2选择性达52.7%,表现出最佳催化效果。     

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.     

Chemical fixation of carbon dioxide to propylene carbonate over amine-functionalized silica catalysts

Amine-functionalized silica catalysts (NH₂/SiO₂, NH(CH₂)₂NH₂/SiO₂ and 1,5,7-triazabicyclo[4,4,0]dec-5-ene/SiO₂ (TBD/SiO₂)), which were characterized by ²⁹Si NMR, elemental analysis, N₂ adsorption–desorption method and indicator dye adsorption, were prepared by ultrasonic technique under mild conditions. Such hybrid solid bases showed high catalytic activity towards CO₂ coupling with epoxide. However, it was found that the reaction conditions had a great influence on the performance. Furthermore, silanols on the surface played an important role in the chemical fixation of CO₂. Based on these, the possible reaction mechanism was proposed for CO₂ coupling with epoxide over such type of catalysts.     

CuO/HZSM-5催化溴甲烷芳构化制备芳烃

采用等体积浸渍法制备了不同负载量（1%~7%）的CuO/HZSM-5催化剂,在固定床反应器中研究了不同反应温度、溴甲烷流量以及CuO负载量对溴甲烷芳构化催化性能的影响。采用SEM、XRD、N₂吸附脱附、TEM、XPS、TG、DSC、NH₃-TPD等技术对反应前后的催化剂进行表征。XRD 结果显示活性组分CuO 在HZSM-5上具有很好的分散性,并且反应后Cu晶型不变。NH₃-TPD 结果显示3%的CuO 负载后,催化剂强酸量增加。在CuO 负载量为3%,温度为360℃,反应空速为240 ml·g^-1·h^-1 条件下得到最高的芳烃收率（22.3%）。XPS 结果显示反应后在催化剂上主要的积炭为石墨碳。催化剂稳定性测试结果表明反应40 h内催化活性没有明显下降。     

Catalytic combustion of methane over a highly active and stable NiO/CeO2 catalyst

In the last decades, many reports dealing with technology for the catalytic combustion of methane (CH₄) have been published. Recently, attention has increasingly focused on the synthesis and catalytic activity of nickel oxides. In this paper, a NiO/CeO₂ catalyst with high catalytic performance in methane combustion was synthesized via a facile impregnation method, and its catalytic activity, stability, and water-resistance during CH₄ combustion were investigated. X-ray diffraction, low-temperature N₂ adsorption, thermogravimetric analysis, Fourier transform infrared spectroscopy, hydrogen temperature programmed reduction, methane temperature programmed surface reaction, Raman spectroscopy, electron paramagnetic resonance, and transmission electron microscope characterization of the catalyst were conducted to determine the origin of its high catalytic activity and stability in detail. The incorporation of NiO was found to enhance the concentration of oxygen vacancies, as well as the activity and amount of surface oxygen. As a result, the mobility of bulk oxygen in CeO₂ was increased. The presence of CeO₂ prevented the aggregation of NiO, enhanced reduction by NiO, and provided more oxygen species for the combustion of CH₄. The results of a kinetics study indicated that the reaction order was about 1.07 for CH₄ and about 0.10 for O₂ over the NiO/CeO₂ catalyst.     

Surface modifications of γ-Al2O3, SiO2 and SnO2 supports by titania grafting and their influence in the catalytic combustion of methane

The influence of the Ti-grafting of γ-Al₂O₃, SiO₂ and SnO₂ over Pd-supported catalysts and the presence of CO₂ as co-feeding, in the catalytic combustion of methane, were investigated. Important modifications in the catalytic performances due to grafting of supports were observed. The grafting method leads to formation of titania nanoparticles on the support surface. The interaction between Ti and support, changes in the size of Pd particles, changes in the acidity of supports could explain the modifications in catalytic performances due to grafting. The catalytic performances depend on the nature of the support and are different when CO₂ is introduced in the feed. CO₂ could play an important role, increasing or inhibiting the catalytic performance.