Chemical looping combustion of biomass-derived syngas using ceria-supported oxygen carriers.

Cu, Ni and Fe oxides supported on ceria were investigated for their performance as oxygen carriers during the chemical looping combustion of biomass-derived syngas. A complex gas mixture containing CO, H2, CO2, CH4 and other hydrocarbons was used to simulate the complex fuel gas environment derived from biomass gasification. Results show that the transfer of the stored oxygen into oxidants for the supported Cu and Ni oxides at 800°C for the combustion of syngas was effective (>85%). The unsupported Cu oxide showed high oxygen carrying capacity but particle sintering was observed at 800°C. A reaction temperature of 950°C was required for the supported Fe oxides to transfer the stored oxygen into oxidants effectively. Also, for the complex fuel gas environment, the supported Ni oxide was somewhat effective in reforming CH4 and other light hydrocarbons into CO, which may have benefits for the reduction of tar produced during biomass pyrolysis.

Synthesis of Co3O4 nanowire arrays supported on Ni foam for removal of volatile organic compounds.

Crystalline Co3O4 nanowire arrays freely supported on Ni foam are successfully synthesized using a template-free method. The effects of reaction time, concentration of reactants, and temperature on the morphology of the nanowires are studied. The results indicate that uniform Co3O4 nanowires could be synthesized at 90 degrees C, and a transformation of the samples' morphology from nanoparticles to nanowires to microrods is observed by controlling the concentration of the reactants. The well-ordered nanowires synthesized under the selected reaction conditions are composed of spinel Co3O4 with diameters of 500-580 nm and lengths of 6-8 microm. These nanowires show good catalytic activity for the ozone catalytic oxidation of toluene.

Fly-ash products from biomass co-combustion for VOC control.

Experiments were conducted in a continuous flow reactor at room temperature to evaluate the elimination of low-concentration toluene in the gas phase to verify if fly-ash products from biomass combustion in an ozonation system could be used in the removal of volatile organic compounds. The fly-ash products from pure biomass combustion (Ash(100)) demonstrated the highest ozonation activities upon the removal of low-concentration toluene (1.5 ppmv), followed by the fly-ash products from co-combustion (Ash(30)) and the coal combustion (Ash(0)). Kinetic experiments showed that the activation energy of the toluene elimination process was substantially reduced with the use of ozone and the reaction intermediates, such as formic acids, aldehydes, etc. Results also showed that the intermediates were reduced with increasing humidity level. The combined use of fly-ash products and zeolite 13X enhanced the removal of toluene to above 90% and suppressed the release of residual ozone and intermediates by holding them in the adsorbed phase.

Catalytic ozonation of toluene using zeolite and MCM-41 materials.

The effects of passing ozone over different zeolite and MCM-41 materials to remove toluene were investigated. Different ozone-to-toluene ratios were used to evaluate the catalytic performance during ozonation. The micro- and meso-porous materials removed about 50% of the toluene via adsorption and another 20-40% was decomposed by ozonation, which was catalytically enhanced by the zeolite and MCM-41 materials. The catalytic reaction portion increased by using a higher ozone inlet concentration and it was further enhanced to around 50% with the use of more adsorbents or with longer residence times. Inside the porous structure of the material, ozone was either decomposed into active atomic oxygen for reactions or converted into oxygen for active site regeneration. The number of Lewis acid sites in the adsorbents for ozone decomposition and byproduct generation during the reactions limit the catalytic activities. Trace amounts of intermediates including aldehydes and organic acids were quantified in the ozonation process. A higher ozone inlet concentration helped to reduce intermediate species formation but it led to more residual ozone in the exhaust. The high adsorption capability of the zeolite and MCM-41 adsorbents could serve as reservoirs for suppressing the release of intermediate species to the exhaust.

Potential use of a combined ozone and zeolite system for gaseous toluene elimination.

This study investigated the performance of a combined ozone and zeolite system in eliminating gaseous toluene which is a major contaminant in many industrial and indoor environments. The hypothesis that the removal of toluene by ozone can be substantially affected by confining the oxidation reaction in a zeolite structure was evaluated. The degradation of toluene seemed to be contributed by the active oxygen atom generated from the decomposition of ozone at the Lewis acid sites in the zeolite 13X. Air containing toluene levels at 1.5, 2 and 3 ppm was injected with ozone in the range of 0-6 ppm before being vented into a fixed amount of 3600 g zeolite 13X with 90 mm bed-length. The experimental results showed that the elimination rate of toluene was significantly enhanced when compared to using zeolite or ozone alone. In particular, over 90% of the 1.5 ppm toluene was removed when 6 ppm ozone was used at 40% relative humidity level. Deactivation of the zeolite 13X after a few hours of reactions under the current experimental conditions was probably due to the adsorbed water, carbon dioxide and the reaction by-products. The residue species left in the zeolite and the intermediate species in the exhaust gas stream were characterized by FT-IR, GC-MS and HP-LC methods, respectively. A distinctive peak of O atom attached to the Lewis acid site at 1380 cm(-1) was found in the FT-IR spectrum and trace amount of aldehydes was found to be the reaction by-products.