Solar Reformers Research Articles

Kinetics of steam reforming of methane on Ru/Al 2O 3 catalyst promoted with Mn oxides

New types of solar heated reformers have been developed in recent years. In these reactors, called volumetric reformers, concentrated solar radiation illuminates directly the catalyst through a transparent window. These solar reformers can operate at higher temperatures (1000–1100 °C) since the surface temperature limit of a regular metal tubular reactor used in the industry is eliminated and a much higher heating rate is feasible. The main restriction, so far, of the solar volumetric reformers to operate at these temperatures is caused by the thermal stability of the current available catalysts. A new catalyst, thermally stable at these temperatures, based on Ru supported on α-alumina and promoted with Mn oxides, has been investigated. The experimental results show that the activity of this catalyst in steam reforming of methane was practically unchanged after operation at 1100 °C for 100 h. The structure of the catalyst was studied by XRD. The fresh sample contained α-Al 2O 3 and MnO 2. Under the reaction conditions at high temperatures MnO 2 is reduced to form Mn 3O 4 and spinel MnAl 2O 4. SEM micrographs show large islands of Mn oxides over α-Al 2O 3 particles. The kinetics of the steam reforming of methane on Ru/(α-Al 2O 3 + MnO x ) catalysts was studied in a flow reactor operated in differential mode at the temperature range of 500–900 °C and total pressure of 1–7 atm. Conversion of methane was 2–8%. The results show that the reaction order with respect to methane is <1 at 450–500 °C and close to 1 at 700–900 °C. The reaction order with respect to steam is negative at all temperature range. The kinetic equation was derived from the mechanism of the steam reforming reaction as developed in this paper. This mechanism involves the following main stages: (a) dissociative adsorption of methane on Ru surface; (b) adsorption of steam on the catalyst support in a molecular form; (c) dissociative adsorption of steam on the Ru surface; (d) oxidation of the surface carbon.

Carbonate Composite Catalyst with High-Temperature Thermal Storage for Use in Solar Tubular Reformers

The composite materials of Ni-applied, porous zirconia balls with molten Na2CO3 salt were examined for use in solar thermochemical reforming of methane as the catalyst with high-temperature thermal storage. The millimeter-sized composite balls were tested on the heat discharge property and the catalytic activity for CO2 reforming of methane in a laboratory-scale reactor. The high heat capacity and large latent heat (heat of solidification) of the composite molten salt circumvented the temperature dropping of the catalyst bed, which resulted in the alleviation of rapid decay in chemical conversion during cooling mode of the reactor. The composite catalyst is expected to realize stable operation in the solar reformer under fluctuation of insolation by a cloud passage.