An improved process is provided for in situ mitigation of coke buildup and porous catalyst used for the processing of hydrocarbon feed stocks. The process exhibits improved catalyst activity over extended periods and the process comprises the pretreatment of hydrocarbon feed stocks to reduce impurities in the feed stocks in the form of peroxides and oxygen compounds that promote the formation of coke precursors, which precursors are typically in the form of olefinic oligomers. The process includes contacting the pretreated feed stream with a suitable catalyst under sub-critical, near-critical and supercritical conditions.