The main characteristic of heavy petroleum feedstock is the high content of resin–asphaltene components, which are prone to coke formation and complicate processing by catalytic methods. Therefore, the development of effective, low-cost redox-active initiator additives for the upgrading of heavy hydrocarbon feedstocks remains a significant technological challenge.

In this study, heavy paraffinic fuel oil was used as the feedstock, while ferrospheres (FS) derived from thermal power plant (TPP) ash were applied as a redox-active initiator additive. The effect of ferrospheres on the yield of fuel fractions (boiling point ≤ 360 °C) and on the transformation of resin–asphaltene components during thermal cracking was investigated.

The results show that the addition of ferrospheres does not lead to a noticeable increase in the yield of fuel fractions; however, it leads to a reduction of the total resin–asphaltene content by approximately 50%. At temperatures of 400–450 °C, the oil fraction yield increases by 5.9–6.7 mass % due to intensified resin decomposition, while at 500 °C it promotes deeper conversion of heavy components, resulting in enhanced formation of gas and solid products. The observed activity of ferrospheres is attributed to the redox properties of hematite and the selective adsorption of resin–asphaltene components on iron oxide surfaces.