Digesting cellulosic biomass in the presence of a slurry catalyst may reduce degradation product formation, but catalyst distribution and retention can be problematic. Digestion methods can comprise: providing cellulosic biomass solids and a slurry catalyst capable of activating molecular hydrogen in a digestion unit; providing a digestible filter aid in the digestion unit; distributing the slurry catalyst within the cellulosic biomass solids using fluid flow; retaining at least a portion of the slurry catalyst in a fixed location using the digestible filter aid; heating the cellulosic biomass solids in the presence of the slurry catalyst, a digestion solvent, and molecular hydrogen, thereby forming a liquor phase comprising soluble carbohydrates; and performing a catalytic reduction reaction on the soluble carbohydrates within the digestion unit, thereby at least partially forming a reaction product comprising a triol, a diol, a monohydric alcohol, or any combination thereof in the digestion unit.