We've documented a number of times that Carbon Monoxide can be manufactured in a pretty direct way, by what might seem the rather self-evident reaction between Carbon Dioxide and hot Coal, as represented by the simple equation: CO2 + C = 2CO; and, as seen for just one instance in:
Solar Power Converts CO2, H2O and Coal to Hydrocarbon Syngas | Research & Development; concerning:
"US Patent 4,177,120 - Photolytic Process for Gasification of Carbonaceous Material; 1979; Process and apparatus are disclosed for converting carbon dioxide to carbon monoxide by subjecting the carbon dioxide to radiation in the presence of carbonaceous material such as coal to form carbon monoxide."