The primary/initial thermal degradation pathway is via intermolecular transglycosylation reactions within the glucose monomers of cellulose. Formation of liquid tar from cellulose can also occur via β-elimination. Under this mechanism, volatile acids (e.g. carboxylic acids) formed from the initial cellulose decomposition are able to attack the remaining cellulose as Bronsted acids thus catalysing heterolytic (ring-opening) reactions.Here, we have studied the effects of acids (H 2 SO 4 , H 3 PO 4 , H 3 BO 3 ) and alkalis (Ca(OH) 2 , NH 4 OH) on the yields of levoglucosan and its derivatives (levoglucosenone, 1,4:3,6-dianhydro-α-d-glucopyranose, 1,6-anhydro-β-d-glucofuranose). It was found that the acids generally decreased the total amount of anhydrosaccharides whilst cellulose infused with the alkalis had increased anhydrosaccharide yields. The results indicate that the β-elimination pathway was catalysed by the presence of acidic species (e.g. H + ions). The extent of cellulose conversion via the β-elimination pathway was dependant on the amount and strength of acid infused within the cellulose matrix. However, the β-elimination route could also be suppressed or controlled by the introduction of a neutralising species (e.g. OH − ions).