Catalytic processes can be made even more efficient and sustainable if catalysts are obtained from renewable materials and/or materials that are otherwise viewed as waste. Because the interactions between species are complex, however, unexpected results may be obtained when using impure feedstocks. This paper provides a brief overview of the work that has been done to use wastes to prepare catalysts, followed by a more detailed review of our work with petroleum coke, biomass, and biosolids for porous carbon development and gasification. In particular, the challenges of using these materials are discussed. For example, petroleum coke is a much denser source of carbon than biomass but it also contains more contaminants. Although biomass is generally cleaner, it contains a significant quantity of volatile species so that yields are lower. Biomass is a renewable source of catalysts that can be used through co-feeding to enhance the gasification of other feeds. Spent catalysts can also be a good source of gasification catalysts. Regardless of the source, the catalytic species (e.g., nickel or potassium) can be deactivated by other species present, including vanadium on the spent catalysts or silicon and aluminum that are present in the co-feed. (C) 2016 Elsevier B.V. All rights reserved.