One-pot synthesis of green-emitting nitrogen-doped carbon dots from xylose

Carbon dots (CDs) are interesting carbon nanomaterials that exhibit great photoluminescent features, low cytotoxicity, and excellent water stability and solubility. For these reasons, many fields are starting to integrate their use for a variety of purposes. The catalytic performance of VOPO4 has been evaluated in the synthesis of nitrogen-doped carbon dots (N-CDs). The synthesis reaction was carried out at 180 °C using VOPO4 as a heterogeneous catalyst for 2 to 4 h of reaction time. After reaction, the N-CDs were purified using a novel method for the protection of the functional groups over the surfaces of the N-CDs. The morphological, superficial, and photoelectronic properties of the N-CDs were thoroughly studied by means of TEM, HRTEM, XPS, and photoluminescence measurements. The conversion of the carbon precursor was followed by HPLC. After three catalytic runs, the catalyst was still active while ensuring the quality of the N-CDs obtained. After the third cycle, the catalyst was regenerated, and it recovered its full activity. The obtained N-CDs showed a great degree of oxidized groups in their surfaces that translated into high photoluminescence when irradiated under different lasers. Due to the observed photoelectronic properties, they were then assayed in the photocatalytic degradation of methyl orange.This research was funded by the Spanish Ministry of Science and Innovation (PID2021-122736OB-C42, PID2021-122613OB-I00) and FEDER (European Union) funds (PID2021-122736OB-C42, P20-00375, UMA20-FEDERJA88)

Selective production of furan from gas-phase furfural decarbonylation on Ni-MgO catalysts.

A series of Ni-MgO catalysts (Ni/Mg molar ratio: 0.1-0.3), prepared by a coprecipitation-calcination-reduction methodology, was characterized and evaluated in the gas-phase hydrogenation of furfural. In all cases, after reduction at 500ºC, nickel species were present as very tiny metal Ni(0) nanoparticles and forming part as Ni(II) of a NiO-MgO solid solution, as inferred from XRD and XPS techniques. The decarbonylation process of furfural was favoured at reaction temperatures as low as 190ºC. The most active catalyst was that with a Ni/Mg molar ratio of 0.25, maintaining a furfural conversion of 96% after 5 h of time-on-stream at 190ºC, by feeding a furfural solution in cyclopentylmethyl ether (5 vol.% furfural) under a H2 stream (H2:furfural molar ratio= 11.5 and WHSV= 1.5 h-1). Furan was the main product, with a yield of 88%, whereas furfuryl alcohol was formed at lower reaction temperature and shorter contact time. However, the catalyst suffers a gradual deactivation during a catalytic test of 24 h, attaining a FUR conversion of 65%, with a furan yield following a similar trend (55%), while FOL was almost negligible (only 6%). The regeneration after calcination led to the sintering of Ni nanoparticles, thus decreasing the furan yield.Spanish Ministry of Economy and Competitiveness (CTQ2015-64226-C03-3-R project), Junta de Andalucía (RNM-1565) and FEDER (European Union) funds. J.A.C. and C.G.S. thank University of Malaga for contracts of PhD incorporation. R.M.T. thanks to the Spanish Ministry of Economy and Competitiveness (IEDI-2016-00743) for the financial support within the I3 program

CDs and N-CDs preparation from xylose and xylose-enriched biomass liquors for methyl orange photocatalytic degradation.

CDs are newly discovered carbon nanoparticles that present unique properties. Each nanoparticle consists of a graphitic lattice core covered by a functionalized surface composed by several polar functional groups attached1,2. Due to this functionalization, CDs exhibit photoinduced electronic transference, fluorescence and up-conversion photoluminescence3. CDs have raised increasing attention for their undemanding synthesis procedure combined with the fact that they have been proved to be non-toxic and can be modified to reach satisfactory quantum yield values. A current tendency in the obtention of CDs is the pursuit of a synthesis method that fulfils the requirements of green chemistry but keeps production costs low. Therefore, CDs obtained from green precursors coming from biomass is an emergent research topic4,3,5,6,7. The most frequent and best-known method for CDs production is hydrothermal or solvothermal method7,3,2.The acidic conditions required by this method are commonly achieved using mineral acids such as HCl; nonetheless, the hydrothermal method is compatible with heterogeneous catalysis, which have been proved in this work. As a consequence of their photoluminescence and electron transfer properties, CDs can work as electron mediators, photosensitizers, as well as photocatalysts by themselves 10. It has been proved that CDs when photo excited are outstandingly good electron donors and electron acceptors, since either electron acceptors or electron donors are able to quench the photoluminescence emitted by CDs effectively 9.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Si-Al nanospheres for the valorization of galactose and agarose into 5-hydroxymethylfurfural.

5-hydroxymethylfurfural (HMF) is a compound that has gained attention to potentially substitute fossil resources in areas such as the polymer industry or the production of energy vectors. HMF is produced from the acid treatment of hexoses, such as glucose or galactose. In this sense, algae biomass has gained interest as it can be grown in both, sweet and salt water and their growth rate and CO2 fixation are several times higher than those of terrestrial plants. Red algae, which are rich in agarose, a galactose and 1,6-dehydrogalactose heteropolymer, can potentially be used as feedstock to produce HMF [1]. Hence, in this work, alumina supported nanospheres have been synthetised and employed as acid catalysts due to their high acidity and porosity that allows the selective conversion of these biomass derived compounds into valuable HMF.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Influence of Lewis and Brønsted acid catalysts in the transformation of hexoses into 5-ethoxymethylfurfural

Several sulfonated polymers, which are typical Brønsted acid catalysts, have been employed in the production of two biofuels: 5-ethoxymethylfurfural (EMF) and ethyl levulinate (EL) as main byproduct, and the catalytic results have been attributed to their different chemical and morphological properties. The Purolite CT275DR attained the best results from 5-hydroxymethylfurfural (HMF) with a 63% EMF yield after 16 h at 100 ◦C thanks to their more abundant superficial acid sites. Moreover, Purolite CT275DR was able to efficiently dehydrate and etherify fructose, with a total EMF plus EL yield of 65% after 24 h at 100 ◦C. When glucose or galactose were used as feedstock, alumina was utilized to provide Lewis acid sites, necessary for the transformation of aldoses in so- lution enabling a combined biofuel yield (EMF plus EL) of 40% from glucose after 24 h at 140 ◦C. With the study of the role of each catalyst, both Brønsted and Lewis acid catalysts (resin and alumina, respectively) were required to obtain considerable EMF yields from aldoses. The reutilization of the catalysts employed for 5 cat- alytic runs demonstrated that Purolite CT275DR suffers no appreciable loss of activity, but alumina showed progressive losses in activity in each cycle due to carbonaceous deposits and catalyst loss.Funding for open access charge: Universidad de Málaga / CBUA This research was funded by the Spanish Ministry of Innovation, Science and Universities (RTI2018-094918-B-C44), FEDER (European Union) funds (RTI2018-094918-B-C44 and UMA18-FEDERJA-171) and Malaga University. Authors thank to Universidad de M ́alaga/CBUA for funding for open access charge. C.G.S. acknowledges FEDER funds for her postdoctoral contract (UMA18-FEDERJA-171). B.T.O. acknowledges the Ministerio de Universidades for his predoctoral contract (FPU20/ 02334

Catalysts Based on Ni and Mg Oxides for the One-Pot Production of High Added-Value Products from Furfural.

A family of NiO-MgO samples with Ni/Mg molar ratio between 0.10 and 0.30 are synthesized by co-precipitation and subsequent calcination. The characterization of the samples show the formation of a solid solution with a periclase structure in such a way that the Ni2+species are poorly reducible. After the reduction of the NiO-MgO samples at 500 °C, the catalysts are tested in the furfural (FUR) hydrogenation to obtain valuable products in a one-pot reaction. The catalysts are highly selective toward tetrahydrofurfuryl alcohol (THFA) with a yield above 50% in most cases as well as 1,2-pentanediol (1,2-PeD) and 1,5-pentanediol (1,5-PeD) with maximum yield of 22 and 23% after 22 h of reaction at 170 °C and 4 MPa of H2, respectively. The present work also suggests the presence of two routes in the furfuryl hydrogenation. The first one is associated with the reduction of furfural to furfuryl alcohol (FOL) and the hydrogenation of the ring yielding THFA. In the second route, once FOL is formed, the furanic ring is open to form 1,2-PeD and 1,5PeD.Funding for open access charge: Universidad de Málaga / CBU

Valorisation of glucose into biofuels and high value-added chemicals using zeolites as catalysts.

Hexose sugars can be valorised under acidic conditions to produce the platform chemical 5-hydroxymethylfurfural (HMF), which can be transformed in a broad spectrum of chemicals with applications as biofuels or monomers for polymers [1]. 5-ethoxymethylfurfural (EMF) is one of the derivatives of HMF useful as biofuel or fuel additive, produced usually from the etherification of HMF with ethanol. However, the high price of HMF is an important drawback for its use as feedstock for the production of EMF, which, together with the low yields and selectivity that are often attained by treating biomass or biomass derived compounds, are limiting its industrial application. In this work, several zeolites with different morphologies and chemical compositions have been employed as acid catalysts for the etherification reaction of HMF and ethanol to produce EMF, as well as the direct conversion of glucose into EMF.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

Influence of Structure-modifying Agents in the Synthesis of Zr-doped SBA-15 Silica and Their Use as Catalysts in the Furfural Hydrogenation to Obtain High Value-added Products through the Meerwein-Ponndorf-Verley Reduction

Zr-doped mesoporous silicas with different textural parameters have been synthesized in the presence of structure-modifying agents, and then characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N2 adsorption-desorption at -196 ºC, NH3 thermoprogrammed desorption (NH3–TPD), CO2 thermoprogrammed desorption (CO2–TPD), and X-ray photoelectron spectroscopy (XPS). These porous materials were evaluated in the furfural hydrogenation through the Meerwein-Ponndorf-Verley (MPV) reaction. The catalytic results indicate that the catalyst synthesized under hydrothermal conditions and adding a pore expander agent is more active and selective to furfuryl alcohol. However, the Zr-doped porous silica catalysts that were synthesized at room temperature, which possess narrow pore sizes, tend to form i-propyl furfuryland difurfuryl ethers, coming from etherification between furfuryl alcohol (FOL) and isopropanol molecules (used as H-donor) by a SN2 mechanism.This research was funded by the Ministry of Economy and Competitiveness (Spain) (grant numbers: CTQ2015-64226-C3-3-R, IEDI-2016-00743), Junta de Andalucía (Spain) (P12-RNM-1565), and FEDER (European Union) funds

Effect of the treatment with H3PO4 on the catalytic activity of Nb2O5 supported on Zr-doped mesoporous silica catalyst. Case study: glycerol dehydration.

We have previously demonstrated the influence of the niobium species over the glycerol dehydration reaction and how the catalyst regeneration by thermal treatment modified the catalytic performance due to the transformation of superficial niobium species. This experimental conclusion encouraged us to find a way to maintain and even improve the catalytic behavior of these Nb-based catalysts. Thus, herein, it is reported the influence of phosphoric acid treatment on 8 wt% Nb2O5 supported on a zirconium doped mesoporous silica (Si/Zr =5 molar ratio) catalyst, varying the Nb/P molar ratio between 0.1 and 1. Catalysts were full characterized and tested in the glycerol dehydration at 325 °C. This acid treatment modifies the nature of species present on the catalyst surface, as inferred from 31P NMR data, where the presence of zirconium hydrogenphosphate was detected. A comprehensive study of the influence of acid properties on the catalytic activity has been carried out. Thus, the selectivity to acrolein was improved, which was attributed to this hydrogenphosphate phase and the catalyst stability was associated to the existence of acid sites of low and moderate strength. The best catalyst was studied at higher reaction temperatures, showing the highest glycerol conversion and achieving an acrolein selectivity of 74%, at 350 °C. This catalyst was also regenerated, maintaining its catalytic activity.Spanish Ministry of Economy and Competitiveness (CTQ2015-64226-C03-3-R project), Junta de Andalucía (RNM-1565) and FEDER (European Union) funds. C.G.S. and A.I.M acknowledge the Ministry of Economy and Competitiveness (Spain) for financial support under the Juan de la Cierva-Formación Program (FJCI-2014-19887) and Ramon y Cajal contract (RYC-2015-17870) respectively. J.A.C. thanks University of Malaga for contract of PhD incorporation. R.M.T. thanks to the Spanish Ministry of Economy and Competitiveness (IEDI-2016-00743) for the financial support within the I3 progra