One-step conversion of low-purity polyolefins to value-added products without pretreatments represents a great opportunity for chemical recycling of waste plastics. However, additives, contaminants, and heteroatom-linking polymers tend to be incompatible with catalysts that break down polyolefins. Here, we disclose a reusable, noble metal-free and impurity-tolerant bifunctional catalyst, MoSx-Hbeta, for hydroconversion of polyolefins into branched liquid alkanes under mild conditions. The catalyst works for a wide scope of polyolefins, including different kinds of high-molecular weight polyolefins, polyolefins mixed with various heteroatom-linking polymers, contaminated polyolefins, and postconsumer polyolefins with/without cleaning under 250°C and 20 to 30 bar H2 in 6 to 12 hours. A 96% yield of small alkanes was successfully achieved even at a temperature as low as 180°C. These results demonstrate the great potentials of hydroconversion in practical use of waste plastics as a largely untapped carbon feedstock.