Heterogeneous catalysts promote reactions at the active sites on their surfaces, so the accessibility of cellulose to internal acidic sites and the dispersion limitation are important limiting factor for the catalytic activity. Heterogeneous catalysts can offer technical advantages related to stability, separation, handling, recycling of catalysts, and reactor design. However, none of the catalysts (metal oxides, zeolites, supported acids, and cation-exchange resins) are highly active and selective under mild conditions [80]. Reaction conditions such as reaction temperature, catalyst loading, and reaction medium are required to be optimized for cellulose hydrolysis with solid catalysts to achieve practical applications.