“…Due to the depletion of conventional oil reserves and increasing energy consumption worldwide, the recovery and upgrading of heavy crude oil resources have received more attention from oil companies and research centers. Steam injection techniques (cyclic steam stimulation, steam flooding, steam-assisted gravity drainage) are the most applied methods for heavy crude oil production, where the application of some catalytic precursors and solvents has allowed for increasing significantly the recovery factor by reducing the content of macromolecules, such as asphaltenes and resins, and increasing the yield of light fractions. , During these processes, the viscosity of heavy crude oil is reduced by composition and structure changes of oil compounds due to a series of reactions in the presence of steam (aquathermolysis), involving cleavage of alkyl chains, carbon-heteroatom bonds, hydrogenation, and heteroatom removal, where active hydrogen is produced in situ by water–gas shift (WGS) reaction and water dissociation. , However, the efficiency of water conversion into hydrogen is limited for the accomplishment of high degrees of hydrogenation of organic substances, and condensed structure compounds with free radicals lead to the formation of secondary resins and asphaltene molecules by polyaddition reactions, resulting in viscosity regression. , In order to increase the performance in these processes and provide additional active hydrogen in the reaction system capable of saturating the formed free radicals, some solvents with hydrogen donation capacity via dehydrogenation/hydrogenation mechanisms (tetralin, decalin, and cyclohexane) have been studied to favor the production of light compounds and inhibit polyaddition reactions. − Consequently, the concentration of free radicals in the reaction system decreases, inhibiting the recombination of generated molecule radicals and thus the viscosity rebounding of heavy crude oil. , …”