A ferrihydrite catalyst composition can comprise a ferrihydrite of a structural promoter metal, a chemical promoter metal and potassium to form an amorphous nanoparticulate. The ferrihydrite catalyst can be formed by dissolving an iron salt, a structural promoter metal salt and a chemical promoter metal salt in water to form an aqueous iron solution. A ferrihydrite solid can be precipitated from the aqueous iron solution by addition of a precipitating agent under conditions such that the ferrihydrite solid is a nanoparticulate. A potassium can be incorporated into the ferrihydrite solid to form a ferrihydrite catalyst precursor. The ferrihydrite catalyst precursor can be calcined to form the ferrihydrite catalyst. A synthesis gas can be readily converted to a fuel product by contacting the ferrihydrite catalyst with the synthesis gas under reaction conditions sufficient to form a fuel product mixture.