Abstract
The synthesis of bulk pure Co3O4 catalysts by different routes has been examined in order to obtain highly active catalysts for lean methane combustion. Thus, eight synthesis methodologies, which were selected based on their relatively low complexity and easiness for scale-up, were evaluated. The investigated procedures were direct calcination of two different cobalt precursors (cobalt nitrate and cobalt hydroxycarbonate), basic grinding route, two basic precipitation routes with ammonium carbonate and sodium carbonate, precipitation-oxidation, solution combustion synthesis and sol-gel complexation. A commercial Co3O4 was also used as a reference. Among the several examined methodologies, direct calcination of cobalt hydroxycarbonate (HC sample), basic grinding (GB sample) and basic precipitation employing sodium carbonate as the precipitating agent (CC sample) produced bulk catalysts with fairly good textural and structural properties, and remarkable redox properties, which were found to be crucial for their good performance in the oxidation of methane. All catalysts attained full conversion and 100% selectivity towards CO2 formation at a temperature of 600 °C while operating at 60,000 h−1. Among these, the CC catalyst was the only one that achieved a specific reaction rate higher than that of the reference commercial Co3O4 catalyst.
Highlights
The objective of this work is to carry out a comprehensive study on bulk Co3 O4 catalysts for the oxidation of lean methane that will include the preparation of a wide number of samples; their extensive characterization (N2 physisorption, X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), H2 -TPR and CH4 -TPRe) of the physical-chemical properties and the examination of its catalytic efficiency under demanding/realistic reaction conditions in terms of gas hourly space velocity (60,000 h−1 ) and presence of water vapor in the inlet stream
The employed synthesis methodologies produced a family of eight bulk Co3 O4 catalysts, which was complemented by a ninth commercial sample
The surface composition of the catalysts was strongly dependent on the synthesis methodology, with the relative Co3+ abundance varying significantly among the studied samples and being somewhat related to the optimization of the textural and structural properties
Summary
Natural gas for vehicles (NGV), known as vehicular natural gas, is the name given to the natural gas applied as fuel for automotive. NGV presents numerous environmental and economic advantages in comparison with traditional liquid fuels (gasoline and diesel), even though it is a fossil fuel. Some estimations value the world reserves of natural gas to be enough for more than 200 years at least, at current production and consumption rate [1]. Natural gas is considered the cleanest available fossil fuel. In this sense, vehicles fueled with NGV produce 20–30% and
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