The hydrothermal conversion of a complex sugars solution comprising glucose, arabinose and xylose with zirconia-based catalysts to produce lactic acid (LA) was studied. Catalysts were synthesized by a simple template-assisted sol-gel method. Alternative template removal procedures, such as re uxing ethanol extraction, were compared to the conventional direct calcination. Acidic properties of catalysts were determined by two different techniques, pyridine temperature-programmed desorption and potentiometric titration with n-butylamine. The extracted catalyst reported the highest speci c surface area (323 m 2 g -1 ), total pore volume (0.21 cm 3 g -1 ), and density of acid sites (1.111 µmol m -2 ) with a signi cant contribution of strong acid sites. On the other hand, the thermal treatment transformed the hydrous zirconia into crystalline tetragonal phase, reducing the speci c surface area and removing most of the acid sites. A four factors experimental design was performed and analyzed by means of response surface methodology (RSM) to maximize the LA production with the extracted catalyst. A molar yield of 61.2 % towards LA and complete sugars conversion were reached at optimal operating conditions: 189 °C, 208 min, 0.5 g catalyst g -1 reactants and 10 bar N 2 . Additionally, tting models for main by-products molar yields (furans, glyceraldehyde, glycolic, formic, acetic and levulinic acids) were obtained with good accuracy prediction. All responses were jointly studied to understand the reaction mechanisms involved in generation of intermediaries and undesired degradation products.
Statement Of NoveltyThis work demonstrates that a sugars solution derived from lignocellulosic biomass can be valorized using a simple and low-cost catalyst obtained by a controlled synthesis technique, avoiding postfunctionalization, severe temperatures or acid/base addition to reaction medium. Yields towards high valueadded chemicals, such as lactic acid, can be substantially improved by optimizing the most in uential operating conditions with mathematical and statistical methods. In contrast to the present research, it is rare to nd in the literature a multiple-response analysis in which not only the main product obtaining but also the undesirable by-products were modeled. Moreover, a mixture of sugars was used as feedstock instead of a simple solution, which more closely resembles the complex reaction systems of real agricultural wastes.