u03b3 alumina silicon carbide and mullite in some instances the conversion of co to co 2 might be enhanced by using catalysts deposited on substrates of higher surface area as long as operating temperatures are not so high as to cause surface area loss lt u02dc 900 u00b0 c in this case the catalyst is deposited in the pores of the substrate where it can be readily contacted with evolving co for conversion to co 2 examples of such substrates include high surface area silica alumina u03b3 alumina and silica a mixture of substrates impregnated with catalysts may usefully be employed in many instances for example a mixture of low surface area sand with high surface area u03b3 alumina both substrates being impregnated with a catalyst may usefully be employed under moderate combustion conditions catalysts which are suitable for use in practicing the invention include noble metals transition metal oxides and alkali metal oxides such as pt nio coo and na 2 o referring again to fig1 a thermocouple 12 provides an indication of temperature to the digital computer 13 when burning solid fuel in accordance with the present invention the temperature in the furnace should be maintained in the range of 400 u00b0 c to 850 u00b0 c the combustor containing the catalytic fluidized bed is charged with the solid fuel this bed is fluidized by the oxidizing gas.