The role of pretreatment in the catalytic valorization of cellulose

The use of fossil resources with the concerning climate change has pushed the development of alternative and sustainable feedstocks for energy, chemicals, and materials production. Lignocellulose is one of the most abundant and promising renewable carbon sources for the transition of a petroleum-based to a bio-based economy. Unlike liquid petroleum oil, the inherent complex polymer structure of the solid lignocellulose makes it recalcitrant for (selective) valorization. Hence, physical and/or chemical pretreatments are usually required to improve the reactivity and/or purity of the feedstock. Promising biorefinery concepts should be able to utilize all components of the lignocellulose. Since cellulose is the most abundant fraction in lignocellulose, this review emphasizes the progress and importance of pretreatment in the conversion of cellulose pulp into chemicals and fuels. The structural and chemical features such as crystallinity, particle size, porosity, and degree of polymerization that influence the reactivity of cellulose are overviewed whenever possible for different reaction types. The advantage and disadvantage of the different approaches for their determination are discussed in detail. The benefits of different pretreatments in bio-chemical and more particularly in chemo-catalytic conversion of cellulose are overviewed. Finally, the future and perspective of (ligno)cellulose pretreatment with regard to cellulose utilization are discussed.