Aquathermolysis of heavy oil using a mixed nickel-oxide/iron-oxide catalyst: Effects induced by crystal phase of iron oxide

Abstract

Nickel and iron compounds have garnered attention as catalysts for upgrading heavy oil via aquathermolysis. However, research on the performance of bimetallic oxide catalysts in aquathermolysis remains limited. To that end, NiO–Fe2O3 catalysts were prepared in this study using a simple physical mixing method and employed in heavy-oil aquathermolysis to investigate the synergistic relationship between NiO and Fe2O3. The product distributions and quality were systematically analyzed, and an asphaltene upgrading index was introduced to evaluate the coke-inhibiting ability of the catalysts. Interestingly, the crystal structure of Fe2O3 in the NiO–Fe2O3 catalysts remarkably influenced the catalytic performance. Particularly, the NiO/α-Fe2O3 catalyst with highly crystalline α-Fe2O3 considerably prolonged the coke induction period up to ∼30% of residue conversion and induced a high deasphalted oil yield from asphaltenes. Moreover, NiO/α-Fe2O3 improved the product quality by removing impurities (S, N, and O) and increasing the H/C ratio. However, the liquid product distribution remained dependent on the thermal cracking effect, as the NiO–Fe2O3 catalysts did not participate in C–C cleavage. Deuterium tracing was performed to elucidate the hydrogen-transfer mechanism in catalytic aquathermolysis. The formation of deuterium–carbon single bonds from catalytic aquathermolysis was three times higher than that in the absence of the catalyst, confirming that NiO/α-Fe2O3 facilitated hydrogen transfer from water molecules to hydrocarbons during aquathermolysis.