It has been known for some time that particles of nickel oxide of less than about 100 nm in size show superparamagnetism that increases as the particle size decreases. The origin of the particle magnetic moment responsible for this behavior has never been fully explained. This research indicated that the size of the particle rather than the presence of nonstoichiometry or impurities of reduced nickel determines the moment. The critical experiment was the measurement of magnetization versus magnetic field for a sample of nickel oxide prepared under conditions that preclude metallic nickel. Almost identical results were found for the original sample, which was black in color and thus nonstoichiometric, and after mild reduction in hydrogen at 400 K, which produced stoichiometry and changed the color to green. The magnetic susceptibility was inversely proportional to the particle size for a given method of preparation. This is consistent with a simple model of incomplete edges on the bounding planes of the crystallite and provides a possible basis for a practical method for measuring particle size in nickel oxide-containing samples.
Biomass pyrolysis and hydropyrolysis have been studied in a high-temperature, high-pressure fluidized bed reactor system. The reactor system can be operated at reaction temperatures up to 982°C (1800°F) and pressures up to 4 MPa (600 psi). Baseline biomass pyrolysis experiments with an inert heat transfer material were conducted at various pressures and hydrogen partial pressures to determine the effect of these variables on product yields and quality, defined by the amount of oxygen in the hydrocarbon-rich liquid product. Biomass hydropyrolysis was performed at temperatures between 375 and 400°C at 2 MPa (300 psi) with selected hydroprocessing catalysts. The most promising catalyst was exposed to 2.9 kg of woody biomass for a total of 21.7 h time on stream over a 10 day period. The cumulative mass balance during this period was 83%, and the overall C 4 + yield was 16 wt %. This corresponds to 31% of the energy in the input biomass feedstock recovered in the hydrocarbon-rich liquid that contained an average of 4.2 wt % oxygen on a dry basis.
Efficient CO 2-utilization is key to limit global climate change. Carbon monoxide, which is a crucial feedstock for chemical synthesis, can be produced by splitting CO 2. However, existing thermochemical routes are energy-intensive requiring high operating temperatures. We report a Hybrid Redox Process (HRP) involving CO 2-to-CO conversion using a lattice oxygen-deprived redox catalyst at relatively low temperatures (<700 °C). The lattice oxygen of the redox catalyst, restored during CO 2-splitting, is subsequently used to convert methane to syngas. Operated at temperatures significantly lower than a number of industrial waste heat sources, this cyclic redox process allows for efficient waste heat-utilization to convert CO 2. To enable the low temperature operation, we report lanthanum modified ceria (1:1 Ce: La) promoted by rhodium (0.5 wt. %) as an effective redox catalyst. Near-complete CO 2 conversion with a syngas yield of up to 83% at low temperatures were achieved using Rh-promoted LaCeO 4-x. While La improves low-temperature bulk redox properties of ceria, Rh considerably enhances the surface catalytic properties for methane-activation. Density Functional Theory calculations further illustrate the underlying functions of La-substitution. The highly effective redox catalyst and HRP scheme provide a potentially attractive route for chemical production using CO 2 , industrial waste heat, and methane, with appreciably lowered CO 2 emissions.
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