CO2 reforming of methane to syngas over highly active and stable Pt/MgO catalysts

Pt/MgO catalysts were prepared by wet impregnation. At 800 °C and atmospheric pressure, Pt/MgO catalysts exhibited a high stability at high gas hourly space velocity of 36,000 ml/g h with a CH₄/CO₂ ratio of 1.0. During 72 h time on stream, the conversion of CH₄ and CO₂ remained almost constant, at about 88% and 90%, respectively. There was no loss of Pt. After reaction, the XRD peaks of MgO became broader, indicating amorphization of MgO, which was supported by TEM results. XPS indicated that the reforming reaction had little influence on Pt. CO₂-TPSR results showed that some carbon deposition occurred under stoichiometric feed of CH₄ and CO₂, but it did not result in the deactivation of the catalyst. The deposited carbon came mainly from the decomposition of methane.     

Potential of zeolite supported rhodium catalysts for the CO2 reforming of CH4

Zeolite Y supported rhodium catalysts were prepared by ion-exchange starting from an aqueous solution of [Rh[(NH₃)₅Cl]Cl₂·6H₂0]. Previous work in this laboratory had shown that this procedure results in a Rh dispersion of near 100%. The catalysts were tested for their activity in the CO₂ reforming of CH₄. They were found to combine extraordinary stability with high activity and selectivity. At 923 K, 90 mol-% of the CH₄ was converted giving a H₂/CO ratio near unity. A weight loading of 0.5 to 0.93% Rh gives the highest turnover frequencies. Thermodynamic equilibrium is reached near 873 K. With a given Rh loading, the zeolite supports are superior to amorphous supports and NaY is superior to the HY. No deactivation was observed in tests of 30 h time on stream at atmospheric pressure or after repeated thermal cycles. No coke deposition was detected by temperature programmed oxidation of used catalysts. Temperature programmed reduction indicates the presence of three discernible Rh species.     

H2 production through steam reforming of ethanol over Pt/ZrO2, Pt/CeO2 and Pt/CeZrO2 catalysts

The effect of the support nature and metal dispersion on the performance of Pt catalysts during steam reforming of ethanol was studied. H₂ and CO production was facilitated over Pt/CeO₂ and Pt/CeZrO₂, whereas the acetaldehyde and ethene formation was favored on Pt/ZrO₂. According to the reaction mechanism, determined by temperature-programmed desorption (TPD) and Diffuse Reflectance Infrared Spectroscopy (DRIFTS) analysis, some reaction pathways are favored depending on the support nature, which can explain the differences observed on the resulting product distribution.     

Role of CeO2 in Ni/CeO2–Al2O3 catalysts for carbon dioxide reforming of methane

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.     

Development of ultra-stable Ni catalysts for CO2 reforming of methane

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 CH_x on Ni surface by oxygen species from CO₂ through dissociation at metal-support interface is a key step for the inhibition of carbon formation.     

Influence of chlorine ions in Pt/A12O3 catalysts for methane total oxidation

Residual chlorine ions on a Pt/Al₂O₃ catalyst surface prepared from chlorine-containing precursors appear to inhibit the total oxidation of methane. At 450°C, as chlorine is eliminated with time on stream, the reaction rate increases despite the sintering of the platinum particles. The steady state reaction rate which is reached after 60 h is identical to that obtained with a catalyst prepared from a precursor containing no chlorine. Whether chlorine is present or not in the initial state of the catalyst does not appear to have an influence on the evolution of the platinum particle size.     

The effect of CeO2 structure on the activity of supported Pd catalysts used for methane steam reforming

Palladium (Pd) supported on CeO₂-promoted γ-Al₂O₃ with various CeO₂ (ceria) crystallinities, were used as catalysts in the methane steam reforming reaction. X-ray diffraction (XRD) analysis, FTIR spectroscopy of adsorbed CO, and X-ray photoelectron spectroscopy (XPS) were employed to characterize the samples in terms of Pd and CeO₂ structure and dispersion on the γ-Al₂O₃ support. These results were correlated with the observed catalytic activity and deactivation process. Arrhenius plots at steady-state conditions are presented as a function of CeO₂ structure. Pd is present on the oxidized CeO₂-promoted catalysts as Pd⁰, Pd⁺ and Pd²⁺, at ratios strongly dependent on CeO₂ structure. XRD measurements indicated that Pd is well dispersed (particles <2 nm) on crystalline CeO₂ and is agglomerated as large clusters (particles in 10–20 nm range) on amorphous CeO₂. FTIR spectra of adsorbed CO revealed that after pre-treatment under H₂ or in the presence of amorphous CeO₂, partial encapsulation of Pd particles occurs. CeO₂ structure influences the CH₄ steam reforming reaction rates. Crystalline CeO₂ and dispersed Pd favor high reaction rates (low activation energy). The presence of CeO₂ as a promoter conferred high catalytic activity to the alumina-supported Pd catalysts. The catalytic activity is significantly lower on Pd/γ-Al₂O₃ or on amorphous (reduced) CeO₂/Al₂O₃ catalysts. The reaction rates are two orders of magnitude higher on Pd/CeO₂/γ-Al₂O₃ than on Pd/γ-Al₂O₃, which is attributed to a catalytic synergism between Pd and CeO₂. The low rates on the reduced Pd/CeO₂/Al₂O₃ catalysts can be correlated with the loss of Pd sites through encapsulation or particle agglomeration, a process found mostly irreversible after catalyst regeneration.     

Control of the product ratio of CO2/(CO+CO2) and inhibition of catalyst deactivation for steam reforming of gasoline to produce hydrogen

Factors controlling the product ratio of CO₂/(CO+CO₂) and methods for inhibiting deactivation of catalyst for steam reforming of gasoline were studied. Syngas (H₂+CO) as major product was produced on Ni-Mo/Al₂O₃ and the major product on Ni-Re/Al₂O₃ was H₂ and CO₂ at the same reaction conditions. Hydrogen with a high CO₂/(CO+CO₂) ratio of about 92% was produced by coupling reaction of steam reforming and water gas shift on Ni-Re/Al₂O₃ catalyst at 805 K. The multifunctional activity of the bimetallic catalyst of Ni-Re/Al₂O₃ and the suitable reaction temperature were of crucial significance for the coupling reaction. Although no deactivation could be observed on both Ni-Mo/Al₂O₃ and Ni-Re/Al₂O₃ catalysts for steam reforming of sulfur-free fuels in about 200 h of time on stream, the activity and sulfur-tolerance of Ni-Re/Al₂O₃ was much better than the values of Ni-Mo/Al₂O₃ for steam reforming of sulfur-containing fuels because of the unique role of rhenium in the Ni-Re catalyst. The unique role of rhenium in Ni-Re catalyst was mainly because of alloying of rhenium with nickel to form bimetallic Ni-Re sites and interaction of rhenium with sulfur to form S-Re binds. The sulfur-tolerance of Ni-Re/Al₂O₃ for steam reforming of sulfur-containing gasoline was improved further by addition of a small amount of ZSM-5. The activity and sulfur-tolerance of Ni-Mo/Al₂O₃ was also enhanced by the addition of ZSM-5.     

CO2 reforming of CH4 over nanocrystalline zirconia-supported nickel catalysts

Mesoporous nanocrystalline zirconia with high-surface area and pure tetragonal crystalline phase has been prepared by the surfactant-assisted route, using Pluronic P123 block copolymer surfactant. The synthesized zirconia showed a surface area of 174 m² g⁻¹ after calcination at 700 °C for 4 h. The prepared zirconia was employed as a support for nickel catalysts in dry reforming reaction. It was found that these catalysts possessed a mesoporous structure and even high-surface area. The activity results indicated that the nickel catalyst showed stable activity for syngas production with a decrease of about 4% in methane conversion after 50 h of reaction. Addition of promoters (CeO₂, La₂O₃ and K₂O) to the catalyst improved both the activity and stability of the nickel catalyst, without any decrease in methane conversion after 50 h of reaction.     

Synthesis of carbon-supported nickel catalysts for the dry reforming of CH4

A series of carbon-based nickel (Ni) catalysts was prepared in order to investigate the effect of the preparation method on the dispersion of Ni and its final catalytic activity in the dry reforming of methane, i.e. CH₄ + CO₂ = 2H₂ + 2CO. Three parameters were studied: (i) the influence of the surface chemistry of the carbon used as support; (ii) the method of drying (conventional vs. microwave drying); and, (iii) the temperature of the reduction stage. In order to study the role of the surface chemistry of the commercial activated carbon used as support, the active carbon was tested as received and oxidized. Although a better Ni dispersion was achieved over the oxidized support, the conversions were much lower. It was also found that microwave drying offers various advantages over conventional drying, the main one being that less time is required to prepare the catalyst. Two reduction temperatures were used (300 and 500 °C), being found that it is necessary to adjust this parameter to prevent the Ni particles from sintering.     

用于甲烷二氧化碳重整新型催化材料的研究进展

甲烷二氧化碳重整因具有环境保护与资源利用的双重效益而备受关注,与其相关的催化材料研究取得了巨大进步。本文回顾了甲烷二氧化碳重整反应催化剂研究方面的主要工作,概述了近年来该领域中新型催化材料的研究进展。     

NiBa catalysts for CO2-reforming of methane

Ni–Ba catalysts supported on γ-Al₂O₃ for the dry reforming of methane were prepared, characterized and studied under reaction conditions. Ba incorporation inhibits the formation of Ni spinel. All the Ni–Ba catalysts studied are highly active for the CO₂-reforming of methane. However, the Ni–Ba catalyst with high Ba and Ni content was the most active and stable catalyst, due to the presence of accessible Ni particles stabilized by the formation of BaAl₂O₄.     

Chemical and microstructural investigation of Pt/CeO2 catalysts reduced at temperatures ranging from 473 to 973 K

The combined application of chemical techniques and HREM shows that platinum deactivation in Pt/CeO₂ catalysts steadily increases with the reduction temperature (T_r: 473–1173 K). Though no suppression of the H₂ adsorption was observed, the TPD-H₂ traces indicate the occurrence of significant chemical changes with T_r. As revealed by HREM, the metal decoration starts at T_r: 973 K, a temperature well above those at which the chemical effects can be observed.     

CO2吸附强化CH4/H2O重整制氢催化剂研究进展

CO_2吸附强化CH_4/H_2O重整制氢是提供低成本高纯氢气和实现CO_2减排的方法之一。其中,催化剂和吸附剂是该工艺的重要组成部分,其活性与选择性制约了反应速率和产率,寿命长短关系到生产成本。综述了CO_2吸附强化CH_4/H_2O重整制氢催化剂和吸附剂的研究现状及存在的问题,机械混合的催化剂与吸附剂在反应过程中存在吸附产物包覆催化活性位点的问题,导致催化剂活性迅速下降。针对该问题,进一步探讨了不同结构双功能复合催化剂的结构特性、研究现状及其在循环-再生过程中存在的问题,核壳型双功能催化剂具有吸附组分与催化剂组分相对独立、催化组分分散分布和比表面积大等优点,在吸附强化制氢中有进一步研究的潜力。利用双功能催化剂的结构特点,实现反复循环再生过程中催化与脱碳反应的匹配,是推动CO_2吸附强化CH_4/H_2O重整制氢技术工业化发展的关键。     

Support effects in Pt/TiO2–ZrO2 catalysts for NO reduction with CH4

ZrO₂–TiO₂ mixed oxides, prepared using the sol–gel method, were used as supports for platinum catalysts. The effects of catalyst pre-reduction and surface acidity on the performance of Pt/ZT catalysts for the reduction of NO with CH₄ were studied. The diffuse reflectance infrared Fourier transformed (DRIFT) spectra of CO adsorbed on the Pt/ZT catalysts, and also on the Pt/T and Pt/Z references, pre-reduced at 773 K in hydrogen, revealed that an SMSI state is developed in the Ti-rich oxide-supported platinum catalysts. However, no shift in the binding energy of Pt 4f_7/2 level for Pt/T and Pt deposited on Ti-rich support counterparts pre-reduced at 773 K was found by photoelectron spectroscopy. The DRIFT spectra of the catalysts under the NO+O₂ co-adsorption revealed the appearance of nitrite/nitrate species on the surface of the Zr-containing catalysts, which displayed acidic properties, but were almost absent in the Pt/T catalyst. The intensity of these bands reached a maximum for the Pt/ZT(1:1) catalyst, which in turn exhibited a larger specific area. In the absence of oxygen in the feed stream, the NO+CH₄ reaction showed DRIFT spectra assigned to surface isocyano species. Since the intensity of this band is higher for the Pt/ZT (9:1) catalyst, it seems that such species are developed at the Pt–support interface.     

Ni catalysts from NiAl2O4 spinel for CO2 reforming of methane

A series of mixed oxides close to NiAl₂O₄ was obtained by a sol–gel like method (propionic acid). The characterization of the different structures was made by X-ray diffraction (XRD), scanning electron microscopy (SEM) or transmission electron microscopy (TEM). For the stoichiometric ratio of Ni to Al exactly equal to 0.5, homogeneous crystalline spinel phase was formed for a temperature of calcination equal or higher than 725 °C. A solid solution was obtained for a Ni/Al ratio lower than 0.5. The spinel structure is non-tolerant concerning a change of nickel to aluminum ratio higher than 0.5: an excess of nickel gives large particles of NiO on spinel phase. Comparative reduction and dry reforming of these oxides was made to control the formation of Ni and its sintering for applications in methane dry reforming. Preliminary reactivity results in dry reforming of methane are given.     

Structure and reactivity of plasma treated Ni/Al2O3 catalyst for CO2 reforming of methane

The glow discharge plasma treated Ni/Al₂O₃ catalyst showed an excellent anti-coke property for CO₂ reforming of methane. Characterizations using X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature programmed reduction (TPR), transmission electron microscopy (TEM), and CO adsorbed infrared spectroscopy (IR) were conducted to investigate the structure and reactivity of the plasma treated Ni/Al₂O₃ catalyst for CO₂ reforming of methane. It confirms that the plasma treatment of Ni precursor at room temperature followed by calcination thermally has a significant influence on the surface characteristics of the active phase. The plasma treated catalyst contains high concentration of close packed plane with improved Ni dispersion and enhanced Ni-alumina interaction, which lead to high catalytic activity and excellent resistance to formations of filamentous carbon and encapsulating carbon.     

Ni基重整催化剂失活机理研究进展

H₂是一种清洁、绿色的燃料和能源载体。目前工业上应用较为成熟的生产工艺是重整反应制氢。其中,Ni基重整催化剂由于其高储量、高活性和低成本的优点而受到研究人员的广泛关注,但在反应过程中存在易因烧结、积炭和中毒等原因而失活的问题。因此,如何提高Ni基重整催化剂的反应稳定性是一个急需解决的问题。本文介绍了上述三种引起Ni基重整催化剂失活的主要原因,并从调控金属Ni粒子粒径、增强金属-载体相互作用、形成晶格氧或表面氧物种以及Ni粒子纳米结构调控四个方面阐述了近年来在抑制失活并提高Ni基重整催化剂反应性能和稳定性领域所取得的研究进展,并且提出优化反应条件、调变化学组成和调控Ni粒子纳米结构将是提高Ni基催化剂在重整反应过程中的稳定性的有效方法。     

Combined CO2 reforming and partial oxidation of n-heptane on noble metal zirconia catalysts

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.     

The oxidizing role of CO2 at mild temperature on ceria-based catalysts

For thermodynamic reasons, CO₂ has always been considered as inert at mild reaction temperatures (300 °C). In this study, we show that CO₂ may be used as a valuable compound for the catalytic combustion of methane (CCM), if ceria-based materials are used as support for the palladium active phase. Adding CO₂ in the feed significantly improves performances of ceria-zirconia supported catalysts. On the contrary, catalytic performances are inhibited on Pd/γ-Al₂O₃. Inhibition can be avoided by mixing the Pd/γ-Al₂O₃ catalyst with some CeO₂ evidencing cooperation phenomena between both catalysts. In situ DRIFTS experiments show that the inhibition of the alumina-supported catalyst is not due to formation of carbonates species. After an in situ reducing pre-treatment, pure CO₂ is able to rapidly oxidize reduced Pd/Ce_0.21Zr_0.79O₂ catalyst at 300 °C. Dissociation of CO₂ on Ce_0.21Zr_0.79O₂ would be responsible for the oxidation process. Thus, CO₂ helps in replenishing the O reservoir (OSC) of the Ce-Zr-O support which is normally consumed by reductants such as CH₄, H₂ or other HC's. XPS experiments show enrichment in oxygen species bound to Ce (Low BE O1s) on the surface of ceria-zirconia when working in the presence of CO₂. Implications of these results on the behavior of ceria-containing catalysts can be important for practical applications, e.g., in automotive exhaust catalysis.