We've documented a number of times that primary Coal tars, or Coal oils, "long known in the art", as they are commonly described, can be utilized as agents of Coal liquefaction and hydrogenation.
And, we've documented from several sources that, in some processes of Coal liquefaction, as in some processes of Carbon Dioxide recycling through reforming with Methane, Carbon settlement and deposition on catalyst surfaces and in catalyst zones can slow and impair the hydrogenation reactions.