A. Field of the Invention
The invention generally concerns the use of bulk metal oxide catalysts capable producing hydrogen (H2) and carbon monoxide from methane (CH4) and carbon dioxide (CO2). In particular, the bulk metal oxide catalyst includes nesosilicate and two or more metals or metal compounds thereof.
B. Description of Related Art
Synthesis gas or “syngas” is a gas mixture that includes carbon monoxide and hydrogen. Syngas is typically used as an intermediary gas to produce a wide range of various products, such as mixed alcohols, hydrogen, ammonia, i-C4 hydrocarbons, mixed alcohols, Fischer-Tropsch products (e.g., waxes, diesel fuels, olefins, gasoline, etc.) methanol, ethanol, aldehydes, alcohols, etc. Syngas can also be used as a direct fuel source, such as for internal combustible engines.
One of the more common methods of producing syngas is by oxidizing hydrocarbon gases such as methane. For instance, the controlled oxidation of methane can be carried out using carbon dioxide, water, or oxygen or a combination of such materials. For industrial scale applications, methane can be reformed into syngas by using steam, such as by the following reaction:CH4+H2O→CO+3H2 The ratio of CO/H2 obtained in steam reforming process is about 0.33. Many applications, however, require a CO/H2 of about 1.0. Such applications include production of aldehydes, alcohols and ammonia. Therefore, the current solution is to remove excess H2 from the produced syngas using separation techniques that can decrease efficient production while simultaneously increasing associated costs. The ratio of CO/H2 may be increased to about 1.0 by dry reforming of methane. In dry reforming of methane, methane is reacted with carbon dioxide or a mixture of carbon dioxide and oxygen as shown in the following equations:CH4+CO2→2CO+2H2 CH4+CO2+½O2→2CO+3H2+H2O
Catalysts are used to increase the rate of the reaction for both of the above reforming reactions. One problem associated with dry reforming (using carbon dioxide) of methane is that current catalysts are prone to sintering, which reduces the active surface of the catalyst. Another problem is supported catalysts that have good stability in retaining their structure and size over few hundred hours, eventually with time start growing in size. Thus, in dry reforming applications, as the particle size of the catalyst increases over time, the propensity to form agglomerations (e.g., coke) in the catalyst pore structure also increases.