A series of Ce x Zr1–x O2 supports with different Ce/Zr molar ratios were utilized for the preparation of gold catalyst used in the selective oxidation of 5-hydroxymethyl-2-furfural to 2,5-furandicarboxylic acid. The used method of gold deposition allows the preparation of gold particles with homogeneous size and shape distribution, a formulation very useful for studies dedicated to revealing the support participation in the reaction. The supports are characterized by Fourier transform infrared spectroscopy using CO as probe molecule, and the sample catalytic activity is thereafter correlated to the support acid site distribution. The possible participation of its Lewis/Brønsted acidity in the reaction mechanism is also proposed.

A series of gold nanoparticles in the 4–40 nm range were prepared, immobilized on activated carbon and further tested, at low base concentration, in the catalytic oxidation of 5‐hydroxymethyl furfural (HMF) to 2,5‐furandicarboxylic acid (FDCA). Gold particles size variation has no influence on HMF conversion but significantly affects product selectivity and carbon balance. This behavior is ascribed to the thermodynamically favorable oxygen reduction reaction on Au(100) faces. As the gold particle size decreases the Au(100)/Au(111) exposure ratio, estimated by using the van Hardeveld‐Hartog model, increases as well as the FDCA selectivity. The smaller the gold particle size the smaller the 5‐hydroxymethyl‐2‐furancarboxylic acid (HMFCA) to FDCA ratio pointing to the gold size dependent behavior of the oxidation of the alcohol function of the HMF molecule.

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A series of gold colloids were prepared and immobilized on commercial activated carbon.The influence of the colloid preparation and stability were studied and related to the gold particle size in the final catalyst. The catalysts show an important activity in the glucose to gluconic acid oxidation reaction, leading to gluconic acid yield close to 90% in base free mild conditions (0.1 MPa O2 and 40ºC). The size-activity correlation and probable mechanism were also discussed. Finally, the viability of the catalyst was tested by recycling it up to four times. IntroductionBiorefinery, defined as the efficient transformation of renewable materials to fuels and intermediate chemicals, and associated to environmental and economic benefits, has driven the research in this area to notable increase in the last decades [1][2][3][4]. Within the renewable materials the vegetal biomass, mostly constituted by carbohydrates, represents around 75% of the total renewable biomass [5]. Among the carbohydrates represented in this biomass the cellulose remains the most attractive fuel precursor, mainly due to its low price, chemical purity and because it is formed only by one monomerglucose [6].After cellulose depolimerazion the subsequent transformation of glucose to valuable compounds involves a variety of processes such as hydrogenation [7], isomerization [8], dehydration [9] and oxidation [10]. Every single mentioned process or a combination of them lead to the formation of different 'platform chemicals'. As an example, the D-Gluconic acid, derived from the oxidation of glucose at anomeric position, results to be an useful food additive and raw material for drugs and biodegradable polymers manufacturing [11,12]. Industrially D-Gluconic acid is produced by enzymatic fermentation process [13,14] for which the principal inconvenient for sustainable largescale production is the necessity of a neutralization step in order to avoid enzymes deactivation by the produced acid [15]. This problem could be solved either by using a base or by the substitution of the enzymes with a heterogeneous catalyst able to oxidize glucose under mild base-free conditions by using either O2 or H2O2 as oxidants [16][17][18][19].Although the use of base (NaOH and a relatively high pH of around 9-9.5) results in increase of heterogeneous catalyst's activity due to particle size stabilization and metal leaching suppression [20][21][22], a decrease in the selectivity to gluconic acid is often observed caused by the glucose to fructose isomerization process [23]. In addition, the formation of gluconate salt instead of pure gluconic acid occurs and entails the need of cost effective post-reaction treatment to obtain the target acid. Therefore, a simple basefree heterogeneously catalyzed process able to produce selectively gluconic acid and avoiding the problems of particle size sintering and metal leaching is highly desirable.Within the catalyst's candidates for such a process, the most promising alternative is nanometric gold. Glucose oxidation has been carried o...

This work is devoted to the study of viability of immobilized gold colloids on carbon as catalysts for the base-free glucose oxidation reaction with a special emphasis made on catalysts' recycling, operational life and possible routes for deactivation/reactivation under batch conditions. The observed catalytic behavior is related to all possible manners of deactivation, like gold metal state changes (particle size agglomeration or leaching), support modifications or active sites blocking by intermediates. In an attempt to recover the initial catalytic activity, the samples are subjected to different treatments such as H2O and NaOH washings and calcination. The failure of the regeneration procedures to recover the initial activity and after detailed catalyst' characterization allows us to find out the main cause of deactivation.

The development of technologies that allow us to reduce CO 2 emissions is mandatory in today's society. In this regard, we present herein a comparative study of CO 2 adsorption over three types of materials: zeolites, layered double hydroxides (LDH), and zeolites coated LDH composites. The influence of the zeolite Si/Al ratio on zeolites sorption capacity along with the presence of mesopores was investigated. By comparing these results with the well-known performance of LDHs, we aim to provide insights on the factors that may influence the CO 2 capture capacity over zeolites, thus providing useful tools for tuning their properties upon post-treatments.

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