Catalytic Performance of Pt/ZrO2 and Pt/Ce-ZrO2 Catalysts on CO2 Reforming of CH4 Coupled with Steam Reforming or Under High Pressure

CO₂ reforming of methane was performed on Pt/ZrO₂ and Pt/Ce-ZrO₂ catalysts at 1073K under different reactions conditions: (i) atmospheric pressure and CH₄:CO₂ ratio of 1:1 and 2:1; (ii) in the presence of water and CH₄:CO₂ ratio of 2:1; (iii) under pressure (105 and 190 psig) and CH₄:CO₂ ratio of 2:1. The Pt supported on ceria-promoted ZrO₂ catalyst was more stable than the Pt/ZrO₂ catalyst under all reaction conditions. We ascribe this higher stability to the higher density of oxygen vacancies on the promoted support, which favors the cleaning mechanism of the metal particle. The increase of either the CH₄:CO₂ ratio or total pressure causes a decrease in activity for both catalysts, because under either case the rate of methane decomposition becomes higher than the rate of oxygen transfer. The Pt/Ce-ZrO₂ catalyst was always more stable than the Pt/ZrO₂ catalyst, demonstrating the important role of the support on this reaction.     

A Novel KCaNi/α-Al2O3 Catalyst for CH4 Reforming with CO2

A potassium and calcium co-promoted nickel catalyst (KCaNi/-Al₂O₃) prepared by a direct impregnation method possessed a high activity, high stability and excellent coke resistance properties in CH₄ reforming with CO₂. XRD, XPS and H₂-TPR characterizations indicated that (i) Ca and K strengthened the interaction between Ni and -Al₂O₃ and promoted the formation of a unique NiAl₂O₄ phase on the surface of the catalyst and (ii) Ca and K increased the dispersion of Ni and retarded its sintering. Coking reactions (CH₄ temperature-programmed decomposition and O₂-TPO) disclosed that K reduced carbon formation via CH₄ decomposition.     

Oscillations in the NO-CO Reaction on Pt(100): NO Decomposition on Island Boundaries

A novel catalyst, Ni/Ce-ZrO₂/-Al₂O₃ has been designed and examined in carbon dioxide reforming of methane. It gives synthesis gas with CH₄ conversion more than 97% at 800 °C and the activity was maintained during the reaction for longer than 40 h. The high stability of the catalyst is mainly ascribed to the beneficial precoating effect of Ce-ZrO₂ resulting in the existence of stable NiO_x species, a strong interaction between Ni and the support, and an abundance of mobile oxygen species in itself. From TPR results, it has been confirmed that NiO_x formation is more favorable than NiO or NiAl₂O₄ formation, resulting in strong interaction between Ni and the support.     

Sol–Gel-Generated La2NiO4 for CH4/CO2 Reforming

A stable La₂NiO₄ catalyst active in CH₄/CO₂ reforming has been prepared by a sol–gel method. The catalyst was characterized by techniques such as XRD, BET, TPR and TG/DTG. The results show that the conversions of CH₄ and CO₂ in CH₄/CO₂ reforming over this catalyst are significantly higher than those over a Ni/La₂O₃ catalyst prepared by wet impregnation and those over a La₂NiO₄/-Al₂O₃ catalyst. The TG/DTG outcome confirmed that the amount of carbon deposition observed in the former case was less than that observed in the latter two cases, a phenomenon attributable to the uniform dispersion of nanoscale Ni particles in the sol–gel-generated La₂NiO₄ catalyst.     

Steam reforming of LPG over Ni and Rh supported on Gd-CeO2 and Al2O3: Effect of support and feed composition

The steam reforming of liquefied petroleum gas (LPG) over Ni- and Rh-based catalysts supported on Gd-CeO₂ (CGO) and Al₂O₃ was studied at 750-900 °C. The order of activity was found to be Rh/CGO > Ni/CGO ∼ Rh/Al₂O₃ > Ni/Al₂O₃; we indicated that the comparable activity of Ni/CGO to precious metal Rh/Al₂O₃ is due to the occurring of gas-solid reactions between hydrocarbons and lattice oxygen () on CGO surface along with the reaction taking place on the active site of Ni, which helps preventing the carbon deposition and promoting the steam reforming of LPG.The effects of O₂ (as oxidative steam reforming) and H₂ adding were further studied over Ni/CGO and Ni/Al₂O₃. It was found that the additional of these compounds significantly reduced the amount of carbon deposition and promoted the conversion of hydrocarbons (i.e., LPG as well as CH₄, C₂H₄ and C₂H₆ occurred from the thermal decomposition of LPG) to CO and H₂. Nevertheless, the addition of too high O₂ oppositely decreased H₂ yield due to the oxidizing of Ni particle and the possible combusting of H₂ generated from the reaction, while the addition of too high H₂ also negatively affect the catalyst activity due to the occurring of catalyst active site competition and the inhibition of gas-solid reactions between the gaseous hydrocarbon compounds and on the surface of CGO (for the case of Ni/CGO).     

Improvement of coke resistance of Ni/Al2O3 catalyst in CH4/CO2 reforming by ZrO2 addition

This work investigates the improvement of Ni/Al₂O₃ catalyst stability by ZrO₂ addition for H₂ gas production from CH₄/CO₂ reforming reactions. The initial effect of Ni addition was followed by the effect of increasing operating temperature to 500–700 °C as well as the effect of ZrO₂ loading and the promoted catalyst preparation methods by using a feed gas mixture at a CH₄:CO₂ ratio of 1:1.25. The experimental results showed that a high reaction temperature of 700 °C was favored by an endothermic dry reforming reaction. In this reaction the deactivation of Ni/Al₂O₃ was mainly due to coke deposition. This deactivation was evidently inhibited by ZrO₂, as it enhances dissociation of CO₂ forming oxygen intermediates near the contact between ZrO₂ and nickel where the deposited coke is gasified afterwards. The texture of the catalyst or BET surface area was affected by the catalyst preparation method. The change of the catalyst texture resulted from the formation of ZrO₂–Al₂O₃ composite and the plugging of Al₂O₃ pore by ZrO₂. The 15% Ni/10% ZrO₂/Al₂O₃ co-impregnated catalyst showed a higher BET surface area and catalytic activity than the sequentially impregnated catalyst whereas coke inhibition capability of the promoted catalysts prepared by either method was comparable. Further study on long-term catalyst stability should be made.     

Improvement of Pt/ZrO2 by CeO2 for high pressure CH4/CO2 reforming

CH₄/CO₂ reforming over Pt/ZrO₂, Pt/CeO₂ and Pt/ZrO₂ with CeO₂ was investigated at 2 MPa. Pt/ZrO₂, which shows stable activity under 0.1 MPa, and Pt/CeO₂ showed gradual deactivation with time at the high pressure. The deactivation was suppressed drastically on Pt/ZrO₂ with CeO₂ prepared by different impregnation order (co-impregnation of Pt and CeO₂ on ZrO₂, and consecutive impregnation of Pt and CeO₂ on ZrO₂). The amount of coke deposition was found insignificant and similar among all the catalysts (including Pt/ZrO₂ and Pt/CeO₂). Catalytic activity after the reaction for 24 h was in agreement with Pt particle size after the reaction for same period, indicating that the difference of the catalytic stability is mainly dependent on the extent of Pt aggregation through catalyst preparation, H₂ reduction, and the CH₄/CO₂ reforming. Pt aggregation and the amount of coke deposition were least pronounced on (Pt–Ce)/ZrO₂ prepared by impregnation of CeO₂ on Pt/ZrO₂ and the catalyst showed highest stability.     

Influence of the oxygen pretreatment on the CO2 reforming of methane on Ni/β-SiC catalyst

The influence of the O₂ pretreatment on the CO₂ reforming of methane to synthesis gas has been investigated with Ni catalysts supported on β-SiC extrudate. The structure and properties of the catalysts were characterised by SEM, TEM and XRD techniques. The pretreatment of the catalyst by a mixture of CO₂ and O₂ significantly improves the catalytic activity for the CO₂ reforming. On the Ni 5 wt.% supported on β-SiC catalyst, the CH₄ conversion has reached 90% with the O₂ pretreatment instead of 80% by direct activation under CO₂/CH₄ mixture. The oxygen pretreatment seems to stabilize the metallic nickel phase instead of NiSi₂.     

Mechanistic aspects of carbon dioxide reforming of methane to synthesis gas over Ni catalysts

A study of the kinetic isotope effect (CH₄/CO₂ CD₄/CO₂) for carbon dioxide reforming of methane to synthesis gas shows that an isotope effect exists with k_{CH 4}/k_{CD 4} ratio of 1.05–1.97, depending on reaction temperature and catalyst applied. The attainment of stable performance over Ni/La₂O₃ catalyst is found to be related to the strong chemisorption of CO₂, weak chemisorption of CH₄ and slow rate of CH_x formation, and fast rate for CH_x removal by oxidation.     

Studies on the Stability of a La0.8Pr0.2NiAl11O19 Catalyst for Syngas Production by CO2 Reforming of Methane

CO₂ reforming of CH₄ was studied over a magnetoplumbite-type hexaaluminate La_0.8Pr_0.2NiAl₁₁O₁₉ catalyst, which showed very high activity for over 300 h without deactivation at 1023 K. This catalyst showed good resistance to carbon deposition, which in this reaction and in CH₄ decomposition was investigated by means of XPS and TEM. It is suggested that nano-tube-like carbon is an intermediate in this reaction and a spillover of carbon from crystalline Ni onto the hexaaluminate oxide occurred during the reaction.     

Partial Oxidation and Dry Reforming of Methane Over Ca/Ni/K(Na) Catalysts

Partial oxidation and dry reforming of methane to synthesis gas over Ca/Ni/K(Na) catalysts have been studied. Effects of temperature, pressure, and oxygen/methane ratios on catalytic activity, selectivity, and carbon formation have been determined. Also reforming of ¹³CH₄ in the presence of CO₂ and Temperature-Programmed Oxidation (TPO) of deposited carbon after the reaction indicated that both methane and CO₂ contribute to carbon formation. The TPO of deposited carbon on Ca/Ni/K catalyst showed that the catalyst consumed a significant amount of oxygen, only a fraction of which was consumed by carbon species on the surface, indicating that the surface oxygen plays a significant role in oxidizing and removing carbon species from the catalyst surfaces     

An optimum NiO content in the CO2 reforming of CH4 with NiO/MgO solid solution catalysts

Reduced NiO/MgO, with a NiO content in the range 9.2–28.6 wt%, was found to be a highly effective catalyst for the CO₂ reforming of CH₄ to CO and H₂ (at 790°C, atmospheric pressure and a space velocity of 60000 cm³g^–1h^–1). For smaller or higher NiO contents, the yield was smaller, being negligible for 4.9 wt%. In contrast to the other reforming catalysts, the new catalyst has high stability, since in the optimum NiO range the CO yield remained unchanged at 95% for 120 h without any carbon deposition. The formation of a solid solution between NiO and MgO, which was demonstrated by both X-ray diffraction and temperature-programmed reduction, is most likely responsible for the high selectivity and stability in a large range of compositions of NiO/MgO.     

Steam reforming of ethanol on Ni–CeO2–ZrO2 catalysts: Effect of doping with copper, cobalt and calcium

Steam reforming (SR) and oxidative steam reforming (OSR) of ethanol were investigated over undoped and Cu, Co and Ca doped Ni/CeO₂–ZrO₂ catalyst in the temperature range of 400–650 °C. The nickel loading was kept fixed at 30 wt.% and the loading of Cu and Co was varied from 2 to 10 wt% whereas the Ca loading was varied from 5 to 15 wt.%. The catalysts were characterized by various techniques, such as surface area, temperature programmed reduction, X-Ray diffraction and H₂ chemisorption. For Cu and Co doped catalyst, CuO and Co₃O₄ phases were detected at high loading whereas for Ca doped catalyst, no separate phase of CaO was found. The reducibility and the metal support interactions were different for doped catalysts and varied with the amount and nature of dopants. The hydrogen uptake, nickel dispersion and nickel surface area was reduced with the metal loading and for the Co loaded catalysts the dispersion of Ni and nickel surface area was very low. For Cu and Ca doped catalysts, the activity was increased significantly and the main products were H₂, CO, CH₄ and CO₂. However, the Co doped catalysts showed poor activity and a relatively large amount of C₂H₄, C₂H₆, CH₃CHO and CH₃COCH₃ were obtained. For SR, the maximum enhancement in catalytic activity was obtained with in the order of NCu5. For Cu–Ni catalysts, CH₃CHO decomposition and reforming reaction was faster than ethanol dehydrogenation reaction. Addition of Cu and Ca enhanced the water gas shift (WGS) and acetaldehyde reforming reactions, as a result the selectivity to CO₂ and H₂ were increased and the selectivity to CH₃CHO was reduced significantly. The maximum hydrogen selectivity was obtained for Catalyst N (93.4%) at 650 °C whereas nearly the same selectivity to hydrogen (89%) was obtained for NCa10 catalyst at 550 °C. In OSR, the catalytic activity was in the order N > NCu5 > NCa15 > NCo5. In the presence of oxygen, oxidation of ethanol was appreciable together with ethanol dehydrogenation. For SR reaction, the highest hydrogen yield was obtained on the undoped catalyst at 600 °C. However, with calcium doping the hydrogen yields are higher than the undoped catalyst in the temperature range of 400–550 °C.     

Activation mechanism of methane-derived coke (CHx) by CO2 during dry reforming of methane – comparison for Pt/Al2O3 and Pt/ZrO2

The reaction of methane-derived coke (CH_x: intermediate of the reforming reaction and also a source of coke deposition) with CO₂ was studied on supported Pt catalysts in relation with CO₂ reforming of methane. Temperature-programmed hydrogenation (TPH) was performed to investigate the reactivity of coke deposition after the catalyst was exposed to CH₄/He at 1070 K. Coke on Pt/Al₂O₃ could be hydrogenated around 873 K, while for Pt/ZrO₂ this was above 1073 K. The results indicate that the reactivity of coke with hydrogen was higher on Pt/Al₂O₃ than on Pt/ZrO₂, which was different from the reactivity of coke towards CO₂. Thus, the reactivity of CO₂ was studied and compared on these catalysts by several technics. The amount of CO evolution was measured during CO₂ flow at 1070 and 875 K. Rate and amount of converted CO₂ were higher on Pt/ZrO₂ than on Pt/Al₂O₃. Pt/ZrO₂ was proven to react with CO₂ to produce CO and active oxygen (CO₂CO+O) (probably on its oxygen defect site) more easily than Pt/Al₂O₃.     

Reforming of Methane with Carbon Dioxide over a Catalyst Consisting of Ruthenium Metal and Cerium Oxide Supported on Mordenite

Reforming of CH₄ with CO₂ proceeds at 400 °C over a catalyst consisting of ruthenium metal and CeO₂ highly dispersed on mordenite. The catalyst, Ru-CeO₂/MZ, is highly active for the reforming of CH₄ under the conditions at which a carbon formation reaction is thermodynamically apt to take place. The reforming selectively forms H₂ and CO. An increase in the weight of the catalyst resulting from carbon deposits was scarcely observed. IR spectra for the catalyst indicate that the reforming proceeds via the formation of the intermediate species such as Ru-CO and Ru-CH_x on the surface of ruthenium. The data of H₂ adsorption support the idea that ruthenium is highly dispersed in Ru-CeO₂/MZ.     

Combined catalytic partial oxidation and CO2 reforming of methane over supported cobalt catalysts

The combined partial oxidation and CO₂ reforming of methane to synthesis gas was investigated over the reduced Co/MgO, Co/CaO, and Co/SiO₂ catalysts. Only Co/MgO has proved to be a highly efficient and stable catalyst. It provided about 94–95% yields to H₂ and CO at the high space velocity of 105000 mlg^–1h^–1 and for feed ratios CH₄/CO₂/O₂=4/2/1, without any deactivation for a period of study of 110 h. In contrast, the reduced Co/CaO and Co/SiO₂ provided no activity for the formation of H₂ and CO. The structure and reducibility of the calcined catalysts were examined using X-ray diffraction and temperature-programmed reduction, respectively. A solid solution of CoO and MgO, which was difficult to reduce, was identified in the 800°C calcined MgO-supported catalyst. The strong interactions induced by the formation of the solid solution are responsible for its superior activity in the combined reaction. The effects of reaction temperature, space velocity, and O₂/CO₂ ratio in the feed gases (while keeping the C/O ratio constant at 1/1) were investigated over the Co/MgO catalyst. The H₂/CO ratio in the product of the combined reaction increased with increasing O₂/CO₂ ratio in the feed.     

Small Amounts of Rh-Promoted Ni Catalysts for Methane Reforming with CO2

Small amounts of Rh-promoted Ni/-Al₂O₃ catalysts possessed higher activity than pure Ni/-Al₂O₃, Rh-Al₂O₃ catalysts and exhibited excellent coke resistance ability in methane reforming with CO₂. XRD, H₂-TPR, CO₂-TPD and coking reaction (via CH₄ temperature-programmed decomposition) indicated that Rh improved the dispersion of Ni, retarded the sintering of Ni and increased the activation of CO₂ and CH₄ on the surface of catalyst.     

Investigation of CH4 Reforming with CO2 on Meso-Porous Al2O3-Supported Ni Catalyst

Meso-porous Al₂O₃-supported Ni catalysts exhibited the highest activity, stability and excellent coke-resistance ability for CH₄ reforming with CO₂ among several oxide-supported Ni catalysts (meso-porous Al₂O₃ (Yas1-2, Yas3-8), -Al₂O₃, -Al₂O₃, SiO₂, MgO, La₂O₃, CeO₂ and ZrO₂). The properties of deposited carbons depended on the properties of the supports, and on the meso-porous Al₂O₃-supported Ni catalyst, only the intermediate carbon of the reforming reaction formed. XRD and H₂-TPR analysis found that mainly spinel NiAl₂O₄ formed in meso-porous Al₂O₃ and -Al₂O₃-supported catalysts, while only NiO was detected in -Al₂O₃, SiO₂, CeO₂, La₂O₃ and ZrO₂ supports. The strong interaction between Ni and meso-porous Al₂O₃ improved the dispersion of Ni, retarded its sintering and improved the activated adsorption of CO₂. The coking reaction via CH₄ temperature-programed decomposition indicated that meso-porous Al₂O₃-supported Ni catalysts were less active for carbon formation by CH₄ decomposition than Ni/-Al₂O₃ and Ni/-Al₂O₃.     

Rh/γ-Al2O3 Catalytic Layer Integrated with Sol–Gel Synthesized Microporous Silica Membrane for Compact Membrane Reactor Applications

An efficient and compact catalytic membrane reactor for reforming of CH₄ was developed by integrating a hydrogen perm-selective silica membrane with an Rh/-Al₂O₃ catalyst layer. The catalytic layer was sandwiched between the outer surface of the -Al₂O₃ support tube and the silica membrane with an aim of improving the heat and mass transfer rates through the system and to simplify the reactor geometry. The system showed improved efficiency for reforming of CH₄ at comparatively lower operating temperatures and steam to C molar ratios than the conventional fixed-bed steam reforming systems. Under optimized conditions, a nearly 25-30% improvement from the equilibrium conversion level was achieved as a result of abstraction of hydrogen from the product stream by the silica membrane integrated with the catalyst layer. The performance of the system was evaluated as a function of various process parameters. Because of the compactness and efficiency, the present system emerges as a promising alternative to the conventional membrane reactors, which possess separate catalytic and membrane units.     

A New Catalytic Transesterification for the Synthesis of Ethyl Methyl Carbonate

The application of a novel Ce_0.5Zr_0.5O₂ mixed oxide prepared by the microemulsion method as a support of Ru catalysts for the reforming of CH₄ with CO₂ originates a high-activity catalytic system with excellent stability under reaction conditions. The support characteristics clearly determine the catalytic stability of Ru catalysts under CH₄ + CO₂ reaction conditions. The introduction of cerium as a promoter in the ZrO₂ structure is shown to improve the catalyst performance by increasing the oxygen mobility in the support and consequently reducing deactivation by carbon deposition during reaction.