Zhaolong Zhang

Carbon dioxide reforming of methane to synthesis gas over Ni/La2O3 catalysts

Carbon dioxide reforming of methane to synthesis gas was studied employing Ni/La2O3 catalysts. It was found that, in contrast to the performance of other nickel-based catalysts (e.g. Ni/Al2O3 and Ni/CaO) which exhibit continuous deactivation with time on stream, the rate over the Ni/La2O3 catalyst increases during the initial 2–5 h of reaction and then tends to be essentially invariable with time on stream, displaying very good stability. X-ray diffraction (XRD) studies reveal that a large CO2 pool, stored in the form of La2O2CO3, is accumulating on the Ni/La2O3 catalyst, following exposure to the CH4/CO2 mixture at reaction conditions. Results of H2- and CO-temperature-programmed desorption reveal that the HNi bond is weakened and CO disproportionation is unfavoured on the Ni/La2O3 catalyst, as compared to the Ni/Al2O3 catalyst. Comparison of H2 and CO uptake and Ni dispersion by XRD shows that H2 and CO uptakes are significantly suppressed, by ca. 3–10 times, suggesting that a large portion of the Ni surface is blocked by lanthanum species. It is proposed that the interaction between Ni crystallites and La2O3 support or La species which are decorating the Ni crystallites is responsible for the unusual chemisorptive and catalytic behaviour observed over the Ni/La2O3 catalyst.

Reforming of methane with carbon dioxide to synthesis gas over supported Rh catalysts

Reforming of methane with carbon dioxide to synthesis gas (CO/H2) has been investigated over rhodium supported on SiO2, TiO2, γ-Al2O3, MgO, CeO2, and YSZ (ZrO2 (8 mol% Y2O3)) catalysts in the temperature range of 650–750°C at 1 bar total pressure. A strong carrier effect on the initial specific activity, deactivation rate, and carbon accumulation was found to exist. A strong dependence of the specific activity of the methane reforming reaction on rhodium particle size was observed over certain catalysts. Tracing experiments (using 13CH4) coupled with temperature-programmed oxidation (TPO) revealed that the carbon species accumulated on the surface of the Rh/Al2O3 catalyst during reforming reaction at 750°C are primarily derived from the CO2 molecular route. The amount of carbon present on the working catalyst surface which is derived from the CH4 molecular route is found to be very small.

Partial oxidation of methane to synthesis gas via the direct reaction scheme over Ru/TiO2 catalyst

AbstractThe partial oxidation of methane to synthesis gas has been investigated over various supported metal catalysts. The effects of operational variables on mass and heat transport resistances were investigated for defining the kinetic regime. It is observed that, in the absence of significant mass and heat transfer resistances, high selectivity (up to 65%) to synthesis gas is obtained over Ru/TiO2 catalysts in the low methane conversion range (

Heat transport limitations and reaction scheme of partial oxidation of methane to synthesis gas over supported rhodium catalysts

X_{O_2 }< 100\%

Partial oxidation of methane to synthesis gas over supported ruthenium catalysts

) whereas only negligibly small selectivity to synthesis gas is observed over all other catalysts investigated under similar conditions. This indicates that the Ru/TiO2 catalyst possesses unique properties, offering high selectivity to synthesis gas formation via the direct reaction scheme, whereas the other catalysts promote the sequence of total oxidation of methane to CO2 and H2O, followed by reforming reactions to synthesis gas. An increase of selectivity to synthesis gas, in the presence of oxygen, is achieved over the Ru/TiO2 catalyst by multi-feeding oxygen, which is attributed to suppression of deep oxidation of H2 and CO.

Performance of Ni/La2O3 catalyst in carbon dioxide reforming of methane to synthesis gas

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 kCH4/kCD4 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 CHx formation, and fast rate for CHx removal by oxidation.

Reforming of Methane with Carbon Dioxide to Synthesis Gas over Supported Rhodium Catalysts: I. Effects of Support and Metal Crystallite Size on Reaction Activity and Deactivation Characteristics

The partial oxidation of methane to synthesis gas over supported Rh catalysts is investigated, paying particular attention to removing heat transport limitations and identifying the reaction conditions within the kinetic-controlling regime. The results obtained suggest that the reaction follows the sequence of total oxidation to CO2 and H2O, followed by reforming reactions to synthesis gas.

Catalytic Partial Oxidation of Methane to Synthesis Gas over Ni-Based Catalysts: I. Catalyst Performance Characteristics☆

The catalytic partial oxidation of methane to synthesis gas is investigated over Group VIII metal catalysts. It is shown that while all catalysts promote methane combustion followed by reforming with H2O and CO2, the Ru/TiO2 catalyst, to a large extent, promotes the direct formation of synthesis gas. The existence of the direct reaction route is probed by steady-state isotopic transient experiments. The extent of the direct route is found to be sensitive to modifications of the TiO2 carrier. FTIR and XANES studies indicate that the unique performance of the Ru/TiO2 catalyst is related to its high resistance to oxidation, which renders high selectivity to synthesis gas in the presence of oxygen.