Metal and metal oxide nanoparticles have attracted increased attention due to their unusual physical and chemical properties. The nature, dispersion, and size of the nanoparticles are key factors in determining the activity and selectivity of the supported catalysts. Supercritical fluid deposition (SCFD) is a promising method to deposit metallic nanoparticles and films on inorganic porous supports. CO 2 is the most commonly used supercritical fluid (sc-CO 2) for material synthesis because it is nontoxic, nonreactive, nonflammable, and inexpensive. This work presents the synthesis of cobalt, nickel, and ruthenium nanoparticles on MCM-41, Al-MCM-41, MCM-48, and activated carbon supports in sc-CO 2. Batch and continuous deposition are studied, with two high-pressure reactor configurations: column or alternative (sandwich). To avoid the length of the bed being too long, the reagents were separated into smaller amounts and placed alternately, keeping the total mass of the precursor and support constant. The prepared samples were characterized by scanning electron (SEM/EDX) and transmission electron microscopy (TEM).
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.
Monometallic Ru/MCM48 and Zr/MCM48 and bimetallic Ru/Zr-MCM48 and Zr/Ru-MCM48 catalysts have been synthesized and tested in the hydrogenation of wheat bran hydrolysates. Catalysts have been characterized by XRD, SAXS, TPR, TPD-NH3, TEM, and N2 adsorption/desorption at 77 K. The hemicellulose fraction has been extracted, hydrolyzed, and purified before the hydrogenation reaction. The purification step mainly consists of the extraction of the sugars in an organic phase and a back-extraction in an acid-aqueous solution. Ru/Zr-MCM48 catalyst exhibited the highest conversions of sugars in the hydrogenation of the purified wheat bran hydrolysate (PWBH), practically unchanged after 5 reaction cycles. Sugar alcohol yields were 73.2% in pentitols and 65.9% in sorbitol. The incorporation of the tetragonal ZrO2 to the MCM48 support has led to a more active and stable catalyst for the hydrogenation of PWBH. Results have shown that this incorporation must be done before the deposition of the Ru(0) phase.
The hydrothermal conversion of a multiple sugars solution (xylose, arabinose and glucose) was studied using high surface ZrO2-based catalysts to produce lactic acid. The catalysts were synthesized by template-assisted sol-gel method and alternative template removal procedures. Samples obtained by template extraction with solvent reported a specific surface area of 323 m2/g, a pore volume of 0.21 cm3/g and a total amount of acid sites of 359 µmol/g. An experimental design was performed to model lactic acid and by-products obtaining around the selected catalyst. The response surface methodology (RSM) was used to optimize the main operating conditions. A mass selectivity of 35.1 % towards lactic acid was found at 183 °C and 212 min. In addition, the reaction mechanisms involved were proposed based on intermediates and degradation compounds detected by HPLC analysis.
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 refluxing 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 specific surface area (323 m2 g-1), total pore volume (0.21 cm3 g-1), and density of acid sites (1.111 µmol m-2) with a significant contribution of strong acid sites. On the other hand, the thermal treatment transformed the hydrous zirconia into crystalline tetragonal phase, reducing the specific 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 N2. Additionally, fitting 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.
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