Heavy oil and bitumen are a potential alternative energy source to conventional light crude. However, utilization of these resources can have significant environmental impact. Downhole upgrading offers the potential to improve recovery, and decrease environmental impact. However, use of catalysts to enhance downhole upgrading is limited by the need for a material that can survive the extreme coking conditions arising from the cracking of heavy oil into lighter oil. In this work the potential of hydrogen donors to improve upgrading and enhance catalyst lifetime was considered. In order to extract detailed information on the catalyst structural evolution during reaction a novel integrated adsorption and thermopnrometry characterization method was used. This technique allows detailed information to be obtained on the spatial arrangement of pores and their connectivity, as well as size distributions. For catalyst operated at the conditions studied, it has been found that coking arises in smaller pores branching off the larger pores providing acccss to the catalyst interior. It has been found that use of different hydrogen donors leads to differential survival of open smaller pores in the catalyst, with tetralin providing better protection than cyclohexane or hydrogen gas.