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Official websites use. Share sensitive information only on official, secure websites. Correspondence: svetlana icmse. Nitric acid treatment resulted in microporous biochars with high surface area, whereas the chemical activation with ZnCl 2 substantially increases the mesoporous surface. Keywords: GVL, levulinic acid, Ru based catalysts, biochar, carbonaceous materials, textural properties. Indeed, LA has been classified as one of the top 12 building blocks issued from biomass, due to its broad spectrum of applications, availability and inexpensive high yield production routes \[ 1 , 3 \]. GVL is a stable and low toxic molecule, which can be used by itself as an excellent aprotic polar solvent, as an intermediate in the synthesis of monomers and polymers, a food ingredient, flavoring agent, in the perfume industry and as an oxygenated gasoline additive \[ 5 , 6 \]. GVL can be further upgraded to 1,4-pentanediol, methyl tetrahydrofuran 2-MTHF , valeric acid \[ 7 \], 2-pentanol \[ 8 \], and 2-butanol \[ 9 \] suitable for monomers and branched hydrocarbons for gasoline, diesel, \[ 10 \] and jet biofuels manufacturing \[ 11 \]. Generally, the levulinic acid HDO reaction follows two dominant intermediate pathways, 4-hydroxypentanoic acid 4-HPA and angelica lactone AGL pathways, differing one from another in the order of reactions Scheme 1 \[ 12 \]. The HPA route is suggested as dominant, as a low activation energy is needed to attach a proton to the ketone group to form alkoxy intemidiate followed by ring closure to generate GVL-OH and finally, GVL after hydroxyl group removal. Then, GVL, unlikely, can be further reduced to 1,4-pentanediol PD \[ 13 \] and subsequently dehydrated to 2-methyltetrahydrofuran 2-MTHF \[ 14 \] or hydrogenated to pentanoic valeric acid via pentenoic acid isomers intermediate \[ 15 \]. In addition, the formation of humins and coke from reaction should be considered. GVL production from levulinic acid via HDO reaction needs bifunctional active sites; one for reduction, usually metallic nanoparticles, and one for dehydration, assured by the presence of acid sites \[ 16 \]. Reported active metals comprise noble metals such as Ru \[ 17 \], Rh \[ 18 \], Ir \[ 19 \], Pt \[ 20 \], and Pd \[ 16 , 21 \] and non-noble metals like Ni \[ 22 \], Cu \[ 23 \], Fe \[ 23 \], and Cr \[ 24 \]. In the presence of Ru, the energy barrier for H-H dissociation is negligible and the intrinsic ability of carbonyl activation is high. Therefore, the hydrophilic character induced by the presence of both carbonyl and OH groups in the aliphatic LA molecule induces easily an interaction with the H-bonded water molecules, enhancing dramatically the GVL production. However, the Ru catalyst activity depends on support nature, catalyst synthesis, and HDO reaction conditions \[ 30 \]. Zeolites, silica, and oxide supports were reported to play an important role in the observed kinetics \[ 31 , 32 \]. On the contrary, carbon-based supports appear to be much more stable and maintain the Ru metal nanoparticles performance over extended periods of operation \[ 33 , 34 , 35 , 36 \]. Within the carbonaceous supports, biochars emerge as excellent support candidates due not only to the involved biomass wastes revalorization processes and low-cost production, but also to the multiple tailoring possibilities. The raw biomass was pre-treated either with HNO 3 , ZnCl 2, or both and finally, activated with CO 2 during the slow pyrolysis process. The catalyst series was generated by subsequent ruthenium impregnation and the relations between pre-treatment procedures, samples properties, and catalytic activities were fully discussed. The samples were compared to a commercially available activated charcoal AC as reference support and to a previously prepared Ru-, Pt-, and Pd-based catalysts, which allowed us to evaluate not only the support but also the metal nature influence. Biochars treatment procedures have been adapted from a previous work \[ 43 \]. Cotton stalks demineralization and washing. After that, the cotton stalks were washed with distilled water several times till there was a neutral pH. Cotton stalks activation. The desired amount of nitric acid treated or untreated bare cotton stalks was saturated with ZnCl 2 solution 20 wt. Cotton stalks pyrolysis. Four cotton stalks samples, labelled as C H cotton and C cotton for demineralized acid and untreated sample and C H Zn cotton or C Zn cotton for ZnCl 2 activated samples, respectively, were loaded into a horizontal tubular oven and submitted to slow pyrolysis under continuous CO 2 flow of mL. The washing process aimed at the removal of the mineral and ZnCl 2 excess as well as some pores opening. The required amount of precursor 1, 2, and 5 wt. The metal content was not labeled for samples containing 1 wt. The samples were measured according to American standard, ASTM D , for carbonaceous solids, using 50— mg of sample in an aluminum vessel. Inductively coupled plasma atomic emission spectroscopy ICP was used to measure the noble metal contents for all carbon supported catalysts. Micrographs were taken with a side mounted Ceta 16M camera. The samples were supported on a holey carbon-coated copper grid without using any liquid. For the establishment of the particle size distribution, close to particles from different micrographs were analyzed. LA hydrodeoxygenation reaction was carried out in a 50 mL Parr autoclave equipped with P. In a typical procedure, 10 mg of supported carbon catalyst and 10 mL of 0. For the screening experiments, the reaction mixture was separated from the catalyst with a syringe filter 0. The levulinic acid conversion, yield and, selectivity to GVL have been obtained from the peak areas previously calibrated with pure standards and calculated as follows:. The variation of the C content fits well the expected composition considering the different treatments. The lower the carbon content the higher the mineral component. The demineralization nitric acid treatment increases the C content but decreases the calculated as difference O content. The latter cannot be used directly as a measurement of the oxidation degree of the resulting biochars due to the presence of other elements mineral or ZnCl 2 leftovers. A similar trend was also found by J. L Santos et al. Higher nitrogen content is found for demineralized cotton stalks samples due to their exposure to nitric acid during the treatment. In addition, the presence of sulfur is detected due more probably to the natural presence of some sulfates as mineral components. What is interesting is the decrease of the sulfur content after ZnCl 2 treatment, indicating a probable reaction between the zinc salt and the sulfur leftovers during the activation procedures. The XRD patterns of the impregnated carbon catalysts are very similar to the parent supports Figure S1. The latter is also confirmed by TEM analysis where a high dispersion and low ruthenium particle size is observed Figure 1. The formation of ZnO during carbonization is detectable for C Zn cotton. After washing, the samples also show the characteristic diffractions of different kinds of SiO 2. The comparison of treated and non-treated samples reveals the disappearance of the characteristic peaks of mineral impurities for the washed pattern, indicating successful demineralization, in good agreement with the CNHS elemental analysis. Finally, the calculated average carbon crystallites size Table 3 indicates similar sizes for the prepared biochars and the commercial AC around 12—15 nm. The textural properties of the prepared catalysts are summarized in Table 2 , where the average pore size varies between 3 and 7 nm for all samples. It is worth mentioning that during the reduction, some functional groups can be transformed to CO, H 2, and CO 2, and they can influence the textural properties. Nevertheless, the most interesting aspect is the variation of the mesoporous surface in the catalysts series. The obtained results for the treated samples indicate that under identical pyrolysis conditions, the specific surface BET area increases in mesoporous fraction in disfavor to the microporous one. In this sense, Kim et al. TEM micrographs of the catalysts shown in Figure 1 confirm the monomodal ruthenium metal distribution for all studied systems. One can speculate that the presence of ash and ZnO traces facilitates the high electron density transfer from the support to the metal and some sintering can take place by the same phenomena. The higher specific surface results in higher metal dispersion with mesopores acting as mass transfer channels for nanoparticules anchoring. The calculated average Ru particle size considering their surface distribution Table 3 ranges from 2. The higher the mesopores population and nitrogen percentage, the lower the average particle size. The dispersion of the active phase is calculated on the basis of particle modeling proposed by Yan \[ 45 \] using the average metal particle size determined by TEM. As expected, the dispersion is inversely proportional to the average particle size: the lower the size, the higher the dispersion. The highest ratio found for the AC sample in comparison to the biochars indicates a high proportion of disordered sp 2 carbon and aromaticity for the former according to the elemental analysis. ICP values are likewise summarized in Table 3. In all cases, values close to the nominal 1 wt. Only 1,4-pentanediol is present as a product of GVL hydrogenation. The absence of intermediates, HPA or AGL, might be related to different causes; the former is rapidly converted to GVL in the moment of its formation and the latter is not formed at mild reaction conditions and, if made, is a molecule of low solubility in these conditions. The absence of 4-HPA is also due to the high energy barrier from an alkoxy intermediate in the gas phase \[ 46 \]. Thus, we detect only GVL and 1,4-pentanediol. These products are presented as Others in the selectivity chart Figure 2 B. Blank tests without solid and bare supports tests not shown were carried out and conversion of LA was not observed, suggesting that the HDO process includes LA adsorption and GVL formation only in the presence of metal active sites. In addition, 2 and 5 wt. These samples were incorporated to briefly highlight the superiority of Ru against Pt and Pd and also to demonstrate that 1 wt. As shown in Figure 2 , Ru is the most active metal in comparison to Pt and Pd and becomes the metal of choice for the levulinic acid HDO in mild reaction conditions. Very plausible explanation is given by a recent theoretical study \[ 46 \]. The latter allows an active and always available hydrogen population before or during the HDO process. In addition, in the aqueous phase, Ru can adsorb and break water via hydrogen bonding and participates in the HDO process by decreasing the energy barrier for hydrogen adsorption \[ 47 \]. The Ru metal loading Influence 1, 2, and 5 wt. No matter the support, the activity increases slowly from 1 to 2 wt. Clearly, the metal loading increase rises the active sites concentration and consequently, the rate of the HDO reaction. The Pd hardness low electronegativity leads to faster LA conversion without diminishing the EA barrier of the HDO steps, thus leading to more secondary reactions, i. The support influence on the catalytic activity was also tested. Support effect over Ru-supported carbonaceous materials in levulinic acid HDO reaction. The catalysts prepared using ZnCl 2 -treated biochars are more active in terms of conversion and GVL yield in comparison to that supported on commercial AC. The higher catalytic activity is usually related to the higher number of available ruthenium active sites. The calculation of TON Table 3 , however, suggests that the highest particle size has the highest specific activity. Nevertheless, we should mention that the model of dispersion considers that all the atoms are available and that no particles are lost within the pore systems, and that obviously is not the case for the microporous biochars. The difference found between the specific activity and the obtained yields suggests that the leading factor is not only the surface but also its availability. On the contrary, an increment in the microporosity percentage has a negative effect on levulinic acid conversion. Piskun et al. Indeed, those sites could participate actively in carbonyl groups adsorption and their conversion either to reaction intermediates or humins. Furthermore, SiO 2 content present as impurity in the AC support can also make the difference by its direct participation in the dehydrations steps. This oxide interacts with Ru sharing protons: i. The LA conversion gradually increases with time for both samples; however, considerable differences are observed within the first minutes. At longer times, the LA conversion increases in favor of product degradation. The performance of several reported Ru carbon catalysts for production of GVL in water is summarized in Table 4. Taking into account the variations in metal charge or reaction parameters, one can conclude that the metal charge does not seem primordial for the reaction. We can also observe that the presence of some heteroatoms like nitrogen increases also significantly the activity of the samples. The heteroatoms allow better Ru anchoring, dispersion, and as a consequence, increased the stability and selectivity of the sample. A continuous increase of conversion and GVL yield are found. Clearly, a high temperature is needed to surpass the energy barrier of the HDO steps and promotes dihydrogen molecules dissolution in the liquid phase. The hydrogenation rate increases with increasing hydrogen partial pressure suggesting a positive order for hydrogen in the reaction rate. Besides, the 1,4-pentanediol product is detected at pressures of 30 bars. That is why the change from 5 to 30 bars tripled the LA conversion. The hydrogen pressure, however, can be maintained at 10 bars as safety low pressure not limiting the reaction evolution and giving satisfactory results after a reaction time increase. Full LA transformation is achieved for concentrations lower than 0. Higher LA concentrations decrease the conversion and GVL yield due more probably to the insufficient number of active sites that process the LA transformation steps. A series of homemade carbon materials were prepared from cotton stalks and used to prepare Ru catalysts. The nitric acid treatment results in a successful demineralization of the biomass component prior pyrolysis, which leads, finally, to a carbonaceous support with a higher surface area mostly microporous. The chemical activation with ZnCl 2 significantly enhances the surface area by increasing the mesoporous surface. The high mesoporous surface and specific area of the biochars promote the anchoring of Ru metal resulting in a low particle size and as a consequence, high catalytic activity. Levulinic acid conversion under 10 bars of hydrogen resulted in high GVL production, the Ru being more active than other platinum group metals. High Ru particle size and high microporous surface are promoters of activity deactivation caused either by pore blocking or by leaching. Validation, C. All authors have read and agreed to the published version of the manuscript. This section collects any data citations, data availability statements, or supplementary materials included in this article. As a library, NLM provides access to scientific literature. Nanomaterials Basel. Find articles by Charf Eddine Bounoukta. Find articles by Juan Carlos Navarro. Find articles by Fatima Ammari. Find articles by Svetlana Ivanova. Find articles by Jose Antonio Odriozola. Ioannis V Yentekakis : Academic Editor. Open in a new tab. Click here for additional data file. Similar articles. Add to Collections. Create a new collection. Add to an existing collection. Choose a collection Unable to load your collection due to an error Please try again. Add Cancel. C cotton. C H cotton. C ZnCotton. C H ZnCotton. This work.

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