Search

Real (RBW) and synthetic brewery wastewater (SBW) were treated by aqueous phase reforming (APR) with different 3%Pt/C catalysts for H2 production from the biomass-derived organic load. APR enabled simultaneous treatment of the wastewater and valorisation to H2 and alkanes of the biomass-derived organic load. In the catalytic APR of SBW, TOC and COD removal was higher than 60% after reaction time of the experiments. The addition of KOH or NaOH to SBW resulted in a slightly lower TOC and COD removal, however higher yields to H2 and percentage of valuable gases were obtained in those cases where KOH was added. Catalyst with basic support and low contribution of micropores showed the best performance in the APR of SBW + KOH (∼50% of H2 and 8.9 mmol H2/g COD). The concentration of anions detected in the liquid effluents varied with the catalysts tested and with the concentration of base, suggesting different reaction pathways. Increasing the concentration of KOH led to CO2-free H2 without significant changes in H2 yield. The results obtained with RBW were in good agreement with those from SBW, although the significantly different behaviour of some catalysts suggests the need of tuning their properties according to the composition of the wastewater.

Pt/C catalysts with varied Pt sizes and distributions were investigated for aqueous-phase reforming (APR) of ethylene glycol (EG) to H2. APR experiments were performed on a continuous-flow fixed bed reactor with a catalyst loading of 1 g and EG feeding of 120 mL h−1 at 225 °C and 35 bar for 7 h. The fresh and used Pt/C catalysts were characterized by XRF, BET, CO chemisorption, TEM, XTEM, and XPS. Catalyst preparation protocols changed Pt characteristics on Pt/C catalysts, leading to a distinguishable H2 production. The rates for EG conversion and H2 production increased linearly with mean Pt size (3–11 nm), while having a volcano relationship with the mean size of agglomerated Pt particles (17–30 nm). Pt with concentrated Pt particles on surface of Pt/C catalysts was more preferable for APR of EG than the homogeneously distributed in catalysts. Optimal performance was obtained over a Pt/C-PR catalyst, which was prepared by precipitation method, showing a superb turnover frequency of 248 molH2 molPt−1 min−1 for H2 production from EG in APR. Besides, Pt/C catalysts also showed excellent stability. These results have shown the promise of Pt/C catalyst for APR of EG, which can be extended for bio-H2 production via APR of biomass-derived oxygenates in waste streams.

This paper reports for the first time on the aqueous phase reforming (APR) of a brewery wastewater, which was synthetically prepared according to a real effluent composition. Home-made Pt (3 wt. %) catalysts supported on different carbon materials, have been tested for this purpose at temperatures of 473 and 498 K. The effects of the supports and the organic load of the wastewater on the results of APR have been evaluated. Well characterized commercial carbons with different pH slurry and porous texture have been used as catalyst supports. A wide range of wastewater organic load has been tested, varying the COD from about 1500 to more than 11,200 mg/L, which corresponded to TOC values around 500 and more than 4000 mg/L, respectively. The highest removal of TOC and COD was observed for catalyst supported on highly mesoporous carbon blacks with virtually no microporosity and high pH slurry. At the lowest wastewater organic load (1531 mg/L CODinitial), TOC and COD removal up 99% was achieved and 93% of the TOC was converted into gases, with H2 and alkanes representing more than 70% of the total gas volume generated. The removal of organic matter in the liquid phase decreased at increasing its concentration in the starting wastewater, although the resulting gas contained a higher percentage of H2. Increasing the temperature allowed a higher TOC and COD removal, gas production, carbon conversion to gas and H2 yield. Some deactivation of the catalysts was observed after five successive uses, which can be attributed to partial blockage of the active Pt sites by carbonaceous deposits. The results obtained allow considering APR as an environmentally promising solution for these biomass-derived wastewaters providing also an interesting way of valorisation to H2-rich gas.

Nitrogen-doped porous carbons were prepared using a chitosan biopolymer as both a carbon and nitrogen precursor and metallic salts (CaCl2 and ZnCl2-KCl) as a templating agent with the aim of evaluating their performance as catalyst supports. Mixtures of chitosan and templating salts were prepared by simple grinding subjected to pyrolysis and finally washed with water to remove the salts. The resulting materials were characterized, showing that homogeneous nitrogen doping of carbon was achieved (7–9% wt.) thanks to the presence of a nitrogen species in the chitosan structure. A lamellar morphology was developed with carbon sheets randomly distributed and folded on themselves, creating slit-shaped pores. Substantial porosity was observed in both the micropore and mesopore range with a higher surface area and microporosity in the case of the materials prepared by ZnCl2-KCl templating and a larger size of mesopores in the case of ZnCl2. Catalysts with well-dispersed Pd nanoparticles (around 10 nm in diameter size) were synthesized using the chitosan-based carbons obtained both by salt templating and direct chitosan pyrolysis and tested in the aqueous phase hydrodechlorination of 4-chlorophenol. The fast and total removal of 4-chlorophenol was observed in the case of catalysts based on carbons obtained by templating with CaCl2 and ZnCl2-KCl in spite of the low metal content of the catalysts (0.25% Pd, wt.).

International audience; This paper addresses the challenges of explaining the behavior of porous carbons in cutting-edge applications related to energy storage, catalysis, photocatalysis, and advanced separation based on reactive adsorption. It is a summary of the outcomes of the extensive discussion which took place during the workshop “Beyond Adsorption-II: new perspectives and challenges for nanoporous carbons,” organized as a satellite event to the International Carbon Conference on July 20th , 2019 in New York. It is not our intention to provide a tutorial on the applications, characterization or performance testing of porous carbons; we would rather like to focus on the controversy of the results and phenomena, on the explanation of findings, and on raising concerns to the growing carbon-researching scientific community about the importance of understanding the features of nanoporous carbons by choosing an appropriate characterization technique that will bring meaningful information. We want to emphasize that nanoporous carbons have unique features ensuring them making a marked advance in science and technology. Even though recent studies have shown their potential in various emerging applications, the origin of such performance is not yet well understood. Thus, scientists are encouraged to focus on a precise characterization of porous carbons using a set of complementary techniques for triggering future technological developments.

Aqueous phase reforming (APR) coupled to catalytic wet air oxidation (CWAO) has been investigated as an approach to remove phenolic compounds from wastewater, converting them into valuable gases. Partial oxidation of phenol was achieved in the first CWAO stage trying to minimize mineralization so to allow a high yield to valuable gases in the second APR stage. APR runs were carried out with different mixtures of compounds corresponding to phenol oxidation pathway (phenol, quinones, long and short chain acids) and representing different degrees of oxidation in CWAO stage. A range of TOC and COD removal (74–90%) was observed in APR stage for the single compounds, with higher removal for long chain acids. Likewise, long chain acids provided with the highest conversion to gases. APR of mixtures rich in acids gave the highest yield to CH4 (11.0 mmol CH4/g TOCinitial). H2 production was low in all cases, due to competing direct conversion of long and short chain acids into CH4. TOC and COD removal from wastewater was similar in APR-CWAO and APR, however the conversion to gases and the yield to CH4 were markedly higher for APR-CWAO, thus overcoming the difficulties previously observed in the direct APR of phenol.

This work shows the application of carbon nanocapsules as carriers for sodium ibuprofen release. Hard templating was used to prepare spherical carbon nanocapsules (mean diameter and thick shell of 690 and 70 nm, respectively), exhibiting both micro and mesoporosity. For comparison purposes, a microporous commercial activated carbon and a home-made mesoporous CMK-3 were also studied. All carbons showed similar drug uptake, although microporous commercial carbon and nanocapsules showed higher uptake at low equilibrium concentration due to higher adsorption potential in micropores. Higher and faster release of sodium ibuprofen was observed for carbon nanocapsules at pH 1.8 and 7.4 for a starting load ca. 250 mg g−1. Subsequent loading of carbon nanocapsules by successive evaporation cycles led to a remarkable load of ca. 6010 mg g−1 thanks to sodium ibuprofen filling the internal void volume. In spite of the very high load a fast release was observed at pH 7.4, reaching a release of ca. 100% of the initial sodium ibuprofen load. However, a much slower and lower release was observed at pH 1.8. Thus, the system developed has interesting features for oral drug administration thanks to low toxicity of porous carbon, low release in gastric medium and important release in intestinal medium.

The present work introduces a new type of improved catalysts based on sepiolite-carbon nanocomposites anchoring Pd nanoparticles. The nanocomposites are prepared by assembly in aqueous media of graphene nanoplatelets (GNP) and the nanofibrous sepiolite under a sonomechanical treatment. The methodology allows the co-assembly of other nanomaterials such as multiwall carbon nanotubes (MWCNT) and Pd nanoparticles, these last ones in situ generated from PdCl2 and further treatment with NaBH4. The presence of silanol groups at the external surface of sepiolite favors the growth and assembly of Pd NP which exhibit a quite narrow size distribution independently of the composition of the prepared sepiolite-carbon nanocomposite. The electrical conductivity of the prepared sepiolite-carbon/Pd materials depends of the composition, being lower in materials with higher content in sepiolite. However, the presence of the clay mineral improves textural properties of the resulting materials. The prepared sepiolite-carbon/Pd nanocomposites were tested as catalysts in the hydrodechlorination (HDC) of 4-chlorophenol (4-CPh) under H2 flux, showing all of them an exclusive selectivity towards phenol, though their catalytic activity depends on their composition. Sepiolite is able to neutralize the evolved HCl, favoring the catalytic process. In addition, the good balance between textural and electrical properties achieved in some of the prepared materials enhances the contact between the catalyst surface and the reagents and also favors the electronic transfer, making this new type of sepiolite-carbon/Pd systems very promising. In fact, the concept here reported could be extended to other catalytic applications where the supported metal acting as active center requires the presence of heat and water resistant conductive supports.

The enhancement of the activity of Pd catalysts for aqueous phase hydrodechlorination (HDC) was studied using N-doped tailored supports. N-Doped (1-1.7 wt% N) and non-doped mesoporous carbon materials with equivalent pore structures were prepared via templating with MSU-F silica. At 30 °C, doping of the support resulted in a higher catalytic activity (26 vs. 49 mmol g-1 Pd min-1 for non-doped and doped supports, respectively) in the removal of 4-chlorophenol from water. However, the activity of the catalyst with non-doped carbon supports increased more with reaction temperature, even being the most active at 70 °C (131 vs. 102 mmol g-1 Pd min-1 for non-doped and doped supports, respectively). The activation energy of the process was found to decrease from 32 to 16 kJ mol-1 due to nitrogen doping of the support. Nitrogen doping of the carbon support is an interesting strategy to prepare catalysts with high HDC activity under mild temperature conditions, whereas non-doped supports are more convenient for the intensification of the process by increasing the reaction temperature, The authors acknowledge Hexion Speciality Chemicals Iberica S.A. for providing them with the resol resin Bakelite® PF9934 FL. The authors acknowledge financial support (CTQ2012-32821, CTQ2015-65491_R) and C. Ruiz-García the PhD grant (BES-2013-066085) from MINECO

The effect of H2 availability in the catalytic reduction of NO3− was studied through experimental tests and theoretical estimations of mass transfer regime for H2, CO2 and NO3−. The experiments were carried out in a fixed bed reactor packed with bimetallic 0.75% (w) Pd-Cu catalysts supported on granular activated carbon at 25 °C. External mass transfer limitations were only significant in the case of H2 and resulted in lower selectivity to NH4+, particularly in the low gas surface velocity range (0.09–0.019 cm/s). Low availability of H2, becoming the limiting reagent for the reaction, contributed to lower selectivity to NH4+ due to lower H:N ratio at the catalyst surface. Decreasing space–time also led to lower selectivity to NH4+, probably due to the neutralization of OH− by the available H+ at catalytic sites, thus controlling local pH and favoring N2 production. Reduction of selectivity to NH4+ was achieved with lower loss of activity and NO3− conversion when gas flow was decreased than when liquid flow was decreased. The results indicate that the design and operation of reactors for the catalytic reduction of NO3− should consider conditions leading to H2 transfer control in order to reduce selectivity to NH4+, even though this could be at the expense of reaction rate and NO3− conversion.

This paper reports on the catalytic performance and deactivation in aqueous phase reforming of wastewater streams for H2 production. Brewery wastewater was chosen as representative of this type of effluent. The effect of catalyst support textural characteristics was evaluated using an activated carbon and different modified supports obtained by infiltration and carbonization of a phenolic resol resin into activated carbon. The effect of active phase was evaluated using Pt and PtRe catalysts with different metal molar ratio. At short time on stream values, Pt catalysts supported on modified activated carbon showed higher H2 production than those supported on unmodified activated carbon, indicating that a lower microporosity facilitates the transport of reactants to catalytic active sites and release of reaction products. Bimetallic PtRe catalysts showed higher activity than Pt, particularly using a metal molar ratio of 1:1, which yielded the highest H2 production (117.2 μmol min−1). Despite the different catalysts tested, early and significant deactivation was observed. The characterization of used catalysts allows postulating the adsorption of organic species and/or coke-like matter deposition on the catalysts surface as main causes of deactivation.

The syntheses of platinum nanoparticles (Pt NPs) using colloidal and microemulsion methods and different reducing agents (methanol, NaBH 4 , and N 2 H 4 ) have been compared systematically. The colloidal synthesis was based on polyvinylpyrrolidone (PVP) as capping agent and water and methanol-water mixtures as reaction media. The microemulsion syntheses were carried out using the water-in-oil (w/o) system formed by dioctyl sulfosuccinate sodium salt (AOT), n -heptane and water. The influence of PVP/Pt, reducing agent/Pt and water/AOT molar ratios was studied. The Pt NPs prepared were characterized by transmission electron microscopy (TEM) and X-ray diffractometry (XRD). Both colloidal and microemulsion syntheses resulted in globular shaped NPs consisting mainly of a single crystal domain with fcc structure. Colloidal synthesis with methanol and NaBH 4 , yielded very stable NPs suspensions with small mean particle size (3–6 nm) and distributions extending from 2 to 10 nm. Narrower size distributions were obtained with NaBH 4 , whereas the use of N 2 H 4 led to oversized particles. The most important synthesis variable was the PVP/Pt ratio. In the case of the microemulsion method, a broader range of NPs mean size was obtained (1–7 nm). A better tailoring of the properties of the NPs was achieved varying the type of reducing agent, the reducing agent/Pt ratio and water/AOT ratio. The conditions for the synthesis of NPs suspensions with well differentiated mean size and distribution were identified.

Nitrogen- or boron-doped carbon submicrospheres with a hollow core and a porous shell were prepared via a template method and tested as supports for Pd/C catalysts. The carbon precursor was a phenol-formaldehyde resin that was generated into a silica template using pyridine, 1,10-phenantroline, and sodium tetraphenylborate as doping agents. The nitrogen and boron atomic percentages in doped carbon reached 0.5–3.6 and 0.03–0.67, respectively. High specific areas of up to 1846 m2/g with an important contribution of mesopores were achieved. The prepared Pd catalysts (1% w) exhibited unique features due to the morphology, porous structure, and doping of the support. The active phase was well-dispersed as nanoparticles with narrow size distribution (

Pd catalysts supported on carbon have interesting features for chlorophenols-bearing water treatment by hydrodechlorination, including high stability, activity, and tunable support. In this work, a set of materials based on reduced graphene oxide (rGO) with different degrees of reduction, surface oxygen groups, nitrogen doping, and specific surface area were decorated with Pd nanoparticles, with diameter average size between 5 and 50 nm. Ethanol, hydrazine monohydrate, and sodium borohydride were used as reducing agents, and Pd(AcO)2 was used as a Pd precursor to obtain Pd/rGO nanocomposites in our developed one-pot synthesis approach. A thorough characterization revealed that a similar degree of reduction was obtained for sodium borohydride at 25 °C and hydrazine at 60 °C, although hydrazine also led to nitrogen doping. Pd nanoparticles were homogenously nucleated on the surface of the GO and the obtained nanocomposites were tested as catalysts for hydrodechlorination of 4-chlorophenol in the aqueous phase. The materials with a higher degree of reduction showed the best specific catalytic activity at 70 °C. However, the turnover frequency (TOF) only increased with the reduction degree for the N-doped Pd/rGO, indicating the important role of the nitrogenous functionalities in the catalytic activity. Therefore, the N doping of Pd/rGO catalysts is a feasible strategy to synthesize catalysts highly active for hydrodechlorination.

This document is the accepted manuscript version of a published work that appeared in final form in Energy and Fuels, © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://pubs.acs.org/doi/abs/10.1021/acs.energyfuels.6b02112, Moringa oleifera seed shells exhibit a unique structure of cross-linked sub-microfibers (0.5-1.5 μm diameter) with a well-connected macroporous network. Controlled pyrolysis (500-800 °C) and cyclic activation of the precursor provided a porous carbon material with a structure that minimizes mass-transfer constraints. Under both slow (10 °C/min-1) and flash pyrolysis, the structure was preserved, while a significant microporosity was developed. By flash pyrolysis (700-800 °C), a material with enhanced characteristics for potential application as a molecular sieve (SDA = 450-470 m2 g-1, and SBET = 5 m2 g-1) was obtained. Cyclic activation of carbonized shells, consisting of an oxygen chemisorption stage (180 °C) followed by a desorption stage in an inert atmosphere (450-900 °C), resulted in a controlled development of microporosity upon successive activation cycles. After 10 activation cycles, respective SDA and SBET values of 1172 and 761 m2 g-1 were obtained. Higher development of the surface area and a wider distribution of micropores was observed when the desorption stage was carried out at 900 °C. The development of the surface area was achieved at low burnoff (22-33%), thus preserving the structure of the material. Thanks to its unique structure, the material obtained exhibited enhanced characteristics for gas sorption as a result of diminished mass-transfer limitations, assessed through the kinetics of carbon dioxide adsorption runs at ambient conditions, The authors greatly appreciate financial support from the Spanish Ministerio de Economía y Competitividad (CTQ2012-32821)

The potential advantages of applying encapsulated ionic liquid (ENIL) to CO2 capture by chemical absorption with 1-butyl-3-methylimidazolium acetate [bmim][acetate] are evaluated. The [bmim][acetate]-ENIL is a particle material with solid appearance and 70 % w/w in ionic liquid (IL). The performance of this material as CO2 sorbent was evaluated by gravimetric and fixed-bed sorption experiments at different temperatures and CO2 partial pressures. ENIL maintains the favourable thermodynamic properties of the neat IL regarding CO2 absorption. Remarkably, a drastic increase of CO2 sorption rates was achieved using ENIL, related to much higher contact area after discretization. In addition, experiments demonstrate reversibility of the chemical reaction and the efficient ENIL regeneration, mainly hindered by the unfavourable transport properties. The common drawback of ILs as CO2 chemical absorbents (low absorption rate and difficulties in solvent regeneration) are overcome by using ENIL systems.

This work is aimed at evaluating the catalytic performance of Pd/C catalysts based on size-controlled nanoparticles (mean size 10-50 nm). Carbon black was used as support and the catalysts were tested in the aqueous phase hydrodechlorination of 4-chlorophenol. The Pd precursor was reduced with a methanol/water (10% vol.) mixture in the presence of PVP (PVP/Pd molar ratio 5-35) as capping agent. The performances of unsupported Pd-PVP colloidal nanoparticle and the catalysts prepared by impregnation of them on the carbon black (ex-situ synthesis), reduction of the precursor in the presence of that support (in-situ synthesis) and wetness impregnation were compared. The ex-situ preparation with less content of PVP (PVP/Pd molar ratio of 5) boosted the activity of the Pd-PVP nanoparticles from 16.8 to 167 mmol gPd - 1 min-1 showing the role of the support in enhancing the catalytic performance. The in-situ synthesis with less content of PVP (PVP/Pd molar ratio of 5) resulted in catalysts with lower activity than that prepared by ex-situ synthesis, although they exhibited higher ability to hydrogenate phenol to cyclohexanone and cyclohexanol, which can be related to the morphology of the nanoparticles synthesized. Regardless of the type of synthesis, as PVP dose in synthesis increased, activity and selectivity to hydrogenation products decreased. High activity values were obtained (20-167 mmol gPd - 1 min-1) taking into account the high mean size of the Pd nanoparticles in the catalysts The SusFuelCat project has received funding from the European Union’s Seventh Framework Programme for research, technological development and demonstration under Grant agreement No. 310490 (www.susfuelcat.eu). The authors greatly appreciate financial support from the Spanish MINECO (CTQ2012-32821)

Coupled hydrogenation and aqueous-phase reforming (APR) was studied as an approach to enhance H2 production from brewery wastewater, where maltose is the main component. Hydrogenation of maltose-bearing wastewater produced essentially maltitol. APR stage was performed over PtPd/C catalysts. Faster catalyst deactivation was observed in the APR of maltose than in the APR of maltitol, especially at high feedstock concentration. Higher H2 selectivity and yield were achieved in the APR of maltitol. The increase of temperature from 175 to 225 °C changed the reaction pathways, favouring the production of C1-C2 alkanes for both feedstocks. Higher selectivity to liquid-phase products was obtained in the APR of maltose, evidencing also reaction routes favouring the formation of solid carbonaceous deposits that lead to higher catalyst deactivation. The coupled process can be considered as efficient since H2 production compensated for H2 consumption in the hydrogenation stage and catalyst durability was increased.

The effect of nitrogen doping of a carbon support on the activity of Pd catalysts in the hydrodechlorination of 4-chlorophenol in water has been studied. Highly mesoporous CMK-3 carbons have been synthesized by infiltration of a commercial resol resin into SBA-15 silica followed by pyrolysis at 700 °C and removal of the template with NaOH. Nitrogen doping was achieved by infiltrating 1,10-phenantroline together with the resin. Equivalent porous texture and Pd nanoparticles size were obtained for the catalysts based on undoped and nitrogen-doped CMK-3 carbons. The catalysts allowed fast 4-chlorophenol hydrodechlorination with exclusive selectivity to phenol. A higher activity was observed at 30 °C for the catalyst with the N-doped support (76-81 mmol·gPd-1·min-1), showing the beneficial effect of nitrogen doping of the carbon supports. The different behavior was also evidenced by the activation energies calculated for the catalysts with undoped (53 kJ·mol-1) and N-doped CMK-3 carbon (36 kJ·mol-1) in the 30 - 70 °C temperature range, The authors thank Hexion Speciality Chemicals Iberica S.A. for providing the resol resin Bakelite PF9934 FL and MINECO for providing financial support (CTQ2012-32821, CTQ2015-65491_R) and for the Ph.D. (BES-2013-066085) grant to C.R.-G

This work analyses the application of aqueous phase reforming as a treatment and valorisation method for fruit juice wastewater enabling production of H2 and alkanes from renewable source. The variables considered were pH, organic load and salinity of wastewater, since they are fluctuant and can affect the performance of biological treatments most commonly used. The experiments were carried out in batchwise, at 493 K and 24–28 bar for 4 h using a 3% Pt/C catalyst. Single compounds (glucose, fructose, citric acid, ascorbic acid, galacturonic acid) and fruit juice wastewater were tested as feedstocks. Organic carbon removal from wastewater was higher in the reforming of glucose and fructose within 7–10 pH range, while for organic acids and fruit juice wastewater a higher removal was obtained at pH 2. H2 yield and selectivity increased at increasing pH, due to better conditions for water-gas shift reaction and abstraction of CO2. H2 production by aqueous phase reforming of fruit juice wastewater was little affected by pH, yielding around 6.6 mmol H2/g initial chemical oxygen demand, in the pH range tested. Alkanes were also produced, with higher proportion of CH4 than other alkanes at high pH (10–12). A wide operation window was observed regarding organic load of fruit juice wastewater, although organic carbon removal declined slightly at the highest loads tested. Salinity did not affect organic carbon removal, while H2 yield decreased from 7.8 to 4.2 mmol H2/g initial chemical oxygen demand at high salinity, probably due to catalyst deactivation. Aqueous phase reforming is proved to be an alternative to biological treatment methods with low sensibility to fluctuations in the characteristics of wastewater.

Aqueous phase 4-chlorophenol hydrodechlorination reaction was used to study the effect of N-doping of activated carbon support on the catalytic activity of Pd catalysts. Activated carbon was doped using pyridine and 1,10-phenantroline, reaching nitrogen contents of 0.42-1.22 and 1.35-4.19 % (w), respectively. All catalysts (0.75 % Pd w, carbon basis) showed relatively large Pd nanoparticles (35-55nm), but they exhibited fast and complete 4-chlorophenol disappearance in batch experiments. In runs at 30°C 4-chlorophenol disappearance was mainly ascribed to hydrodechlorination, although N-doping of the support also increased adsorption. Catalysts with supports doped with pyridine yielded higher 4-chlorophenol disappearance rate in spite of lower bulk nitrogen content, however they showed higher concentration of nitrogen species at the external surface and lower loss of surface area during the doping. 4-chlorophenol disappearance rate was boosted at 60°C, with minor differences between catalysts with undoped and N-doped supports, but generation of cyclohexanone was only observed for the ones with doped support. Phenol generation simultaneous to 4-chlorophenol disappearance was observed with all the catalysts. However, subsequent hydrogenation to cyclohexanone ocurred only with the catalysts supported on N-doped activated carbon, The authors greatly appreciate the financial support of this research from the Spanish Ministry of Economy and Competitiveness through the project CTQ2012-32821

A novel method for the preparation of stable Pt/C catalysts with size-controlled nanoparticles has been developed. The method is based on in situ synthesis of the nanoparticles (reduction with NaBH4 in the presence of a support and PVP). Compared to the conventional ex situ route (colloidal synthesis followed by impregnation), this in situ route yields smaller nanoparticles (2.5–3.9 nm) of narrower size distribution. The catalysts prepared by the in situ synthesis showed a higher stability in water at 80 °C, indicating a stronger interaction between the support and the metallic phase. Hydrothermal stability tests were also conducted under conditions equivalent to those of aqueous phase reforming (200 °C, 17 bar and water and diluted acetic acid). Hydrothermal treatment proved to be an excellent method to improve the resistance to leaching of the catalysts. Metal loss was negligible while PVP was almost completely removed from the catalyst; hence, most of the porosity was recovered and the dispersion measured by CO chemisorption increased from 5 to 34–75%. Water at 200 °C was more effective than diluted acetic acid for the removal of PVP. TEM images confirmed that the Pt nanoparticles did not undergo significant changes either in size or morphology upon the hydrothermal treatment, and XPS analysis showed a homogeneous distribution of Pt nanoparticles within the catalyst granules.

Colloidal bimetallic PdRh nanoparticles (NPs) of controlled size and structure were synthesized and tested as catalysts models in aqueous phase hydrodechlorination (HDC) (303. K, 1. atm) using 4-chlorophenol (4-CP) as target compound. The colloidal bimetallic PdRh NPs were synthesized by chemical reduction, using methanol as reducing agent and poly(. N-vinyl-2-pyrrolidone) (PVP) as capping agent. Two methods of synthesis (co-reduction, successive reduction) and three different Pd/Rh nominal molar ratios (0.2, 1, and 5) were used. The NPs were characterized by means of TEM, HAADF-STEM/EDS and XPS.High 4-CP conversion values (85-100%) were achieved at very low metal concentration (1.23×10-3gL-1). Phenol, cyclohexanone, cyclohexanol, and cyclohexene were the reaction by-products detected. Core-shell and cluster-in-cluster NPs structures were obtained by varying the method of synthesis and the Pd/Rh molar ratio. The activity was found to increase with the Pd/Rh ratio. Activity values up to 67.0mmolg-1min-1, which are significantly higher than those obtained in previous works with monometallic Pd (39.1mmolg-1min-1) and Rh (29.4mmolg-1min-1) under equivalent conditions, were achieved. Significant differences in activity and selectivity were found between the NPs with Pd/Rh ratios of 0.2-1 synthesized by co-reduction and successive reduction. The results indicate that the study of the performance of Pd/Rh bimetallic catalysts in HDC requires some consideration about the structure of the NPs, since the metal arrangement can determine an enhancement in the activity of the catalysts.

Nitrogen-doped carbons (NDCs) were prepared by co-pyrolysis of low density polyethylene (LDPE) and tested in the aqueous phase catalytic hydrodechlorination (HDC) of 4-chlorophenol (4-CP). The NDCs were obtained as clusters of non-porous spherical particles with carbon black-like structure. Pyridine and 1,10-phenanthroline were used as nitrogen precursors. Both precursors allowed incorporating a significant content of nitrogen into the carbon matrix (0.1–1.7%, w), with a preferential allocation at the outer regions in the case of pyridine. Different pyrolysis conditions were tested to address their effect on the amount of nitrogen incorporated to the carbon structure. Nitrogen showed different bonding configurations: pyridine-like, pyrrole-like and quaternary. Those NDCs prepared with phenanthroline showed higher content of quaternary and lower of pyrrolic nitrogen in their structure. The NDCs exhibited some activity in HDC, showing their potential as metal-free catalysts. Pd/NDCs catalysts were also prepared and tested. They yielded a much higher activity than Pd supported on non-doped carbons used as blanks, thus suggesting a synergistic between the NDCs and Pd. The NDCs-supported Pd catalysts prepared from 1,10-phenanthroline exhibited a remarkable activity of 55.6 mmol gPd−1 min−1, which may be related to the higher amount of nitrogen of the support with a higher contribution of quaternary nitrogen species.

In the current work, an exploratory study on the application of catalytic aqueous phase reforming (APR) to the treatment of fish-canning wastewater was performed for the first time. Pt/C (3%, w) catalysts were supported on different commercial carbon supports (two activated carbons and a carbon black) and tested in the APR of tuna-cooking wastewater. The effect of the supports and the reaction systems (batch vs. semi-continuous) on the performance of the catalysts was tested. The stability of the catalysts upon 3 successive reuse cycles was checked. TOC and COD removal ranged within 45-60%, which was ascribed to adsorption on the supports, hydrothermal carbonization and APR. The percentage of valuable gases (H2 and alkanes) reached up to 18% of the gas production showing the potential of APR for the valorization and treatment of wastewater. The production of gases is affected by the high chloride, acetate and phosphate concentrations, which may provoke catalyst deactivation. The use of a catalyst with a basic support significantly increased the production of gases and the H2 percentage in the gas fraction. Gas production was higher in semi-continuous compared to batch operation, maybe because the withdrawn gas displaces the reaction towards the products. The percentage of alkanes in the gas phase decreased upon successive catalyst reuse cycles at the expense of H2, which is probably due to sintering of Pt nanoparticles with the corresponding decrease of the number of low-coordinated Pt sites promoting methanation reactions, The authors greatly appreciate financial support from Spanish MINECO (CTQ2015-65491-R). A. S. Oliveira thanks the Spanish MINECO for a research grant (BES-2016-077244)

A novel approach based on Encapsulated Ionic Liquids (ENILs) is proposed for overcoming the mass transfer constraints in CO2physical absorption by ILs. Absorption process simulation using COSMO-based/Aspen Plus methodology -an a priori approach- was carried to select four ILs with high and similar CO2absorption capacity but markedly different transport properties: EmimTCM, BmimTCM, BmimDCN, and BmimOcSO4. Simulations using equilibrium- and rate-based column models for these ILs showed that CO2recovery and the absorbent performance are severely reduced when the viscosity of the IL increases. Experimental gravimetric analyses with the selected ILs confirmed the large differences in solubility and absorption rate, this last also dependent on viscosity. ENILs were prepared by encapsulation of ILs in hollow carbon sub-microcapsules with a porous shell. The experimental gravimetric analysis evidenced that the ILs maintain their CO2absorption capacity after encapsulation, whereas the absorption rate is ca. 50 times higher for ENILs than neat ILs. ENIL tests in fixed bed operation at different operating conditions yielded bed utilization values dependent on the CO2solubility in the ENIL, while equivalent mass transfer zone lengths were obtained for all the materials. The results demonstrate the fast CO2mass transfer rates in ENILs -related to the high contact area provided- allows overcoming the mass transfer limitations controlling the CO2rate of physical absorption by ILs., The authors are grateful to Comunidad de Madrid (project S2013-MAE-2800) and Ministerio de Economía y Competitividad of Spain (project CTQ2017-89441-R) for financial support and Centro de Computación Científica de la Universidad Autónoma de Madrid for computational facilities. Marcos Larriba also thanks MINECO for awarding him a Juan de la Cierva-Formación Contract (Reference FJCI-2015-25343).

This work analyses the stability of a palladium on activated carbon (Pd/AC) catalyst in the ambient-like conditions hydrodechlorination (HDC) of the organochlorinated herbicides 4-chloro-2-methylphenoxyacetic acid (MCPA) and 2,4-dichlorophenoxyacetic acid (2,4-D) as well as 2,4-dichlorophenol (2,4-DCP), a precursor in the synthesis of the second. Continuous long term experiments (100 h time on stream) were performed at mild operating conditions (30 °C, 1 atm). The composition of the reaction effluents was analyzed and their ecotoxicity (Microtox) measured. In all cases, a significant decrease of ecotoxicity was observed due to the high dechlorination achieved. The Pd/AC catalyst maintained a constant activity along the HDC of 2,4-DCP, while it suffered an important deactivation in the HDC of 2,4-D and MCPA. From characterization of the fresh and used catalyst the adsorption/deposition of reaction byproducts on the active sites can be recognized as the main cause of deactivation. The use of activated carbon as support reduces the negative effect that the released chloride ions usually provoke on other HDC catalysts.

In this work a kinetic analysis based on the two-step reaction and Langmuir–Hinshelwood mechanisms is applied to the aqueous phase hydrodechlorination of 4-chlorophenol catalyzed by unsupported Rh nanoparticles. The theoretical predictions of the models based on the two-step and Langmuir–Hinshelwood methods showed good agreement with experimental activity data (turn over frequency) from reaction runs carried out at 303 K with nanoparticles of different sizes (1.9–4.9 nm). The theoretical maximum activity (29–30 h−1) was predicted for nanoparticle sizes of 2.5–2.7 nm, very close to experimental values (ca. 28 h−1, 2.8 nm). The applicability of the two-step reaction and Langmuir–Hinshelwood mechanism to unsupported metal nanoparticles is proved and mechanistic information is obtained. An important difference in the Gibbs replacement adsorption energy (100–130 kJ mol−1) of hydrogen by chlorophenol has been found between edges and terraces.

Pd colloids stabilized with polyvinyl alcohol (PVA) and polyvinylpyrrolidone (PVP) have been prepared, characterized with TEM, zeta potential measurements, CO chemisorption in aqueous phase, and ATR-IR spectroscopy using CO as a probe molecule, and finally tested for performance in nitrite hydrogenation as unsupported nanoparticles. Polymer coverage on Pd surface was significant for both Pd-PVA and Pd-PVP colloid, blocking active sites. The turnover frequency (TOF) of the remaining sites as well as selectivity to ammonium was not influenced by coverage of the Pd surface with PVA. However, the ammonium selectivity increased with increasing Pd particle size. In contrast, increasing coverage of Pd surface with PVP increased the TOF, while the ammonium formation was suppressed. This has been attributed to an effect of PVP on the surface reaction intermediates, based on the observation that chemisorbed CO was also influenced by PVP.

Granular activated carbons were obtained from grape seeds by pyrolysis at 600°C and subsequent physical activation with CO2 (750–900°C, 1–3 h, 25–74% burn-off). The carbon and ash content increased during the activation, reaching values of 79.0% and 11.4%, respectively. Essentially microporous materials with BET surface areas between 380 and 714 m2/g were obtained. The performance of the activated carbon in the adsorption of diuron in aqueous phase was studied within the 15–45°C temperature range. Equilibrium data showed that the maximum uptake increased with temperature from 120 to 470 µmol/g, also evidencing some dependence of the adsorption mechanism on temperature. Data were fitted to five isotherm models [Langmuir, Freundlich, Dubinin–Radushkevich, BET, and GAB (Guggenheim, Anderson, and de Boer)]. Kinetic data were analyzed using first- and second-order rate equations and intraparticle diffusion model. The second-order rate constant values obtained (2.8–13.5 × 10−3 g/µmol min) showed that the hollow...

Catalysts consisting of Pd supported on virgin and heat-treated carbon blacks (homemade and commercial), graphites (natural and synthetic) and commercial carbon nanofibers were prepared and tested in the aqueous phase hydrodechlorinaton (HDC) of 4-chlorophenol (4-CP) under near ambient conditions (30 °C, 1 atm) in order to explore the effect of the support on the catalytic behavior. The homemade graphitized supports were prepared from commercial carbon black (CB) and from a carbon black-like material (CBPE) obtained from pyrolysis of low-density polyethylene. All the catalysts prepared yielded complete 4-CP conversion, although a wide range of activity was observed (10.7–173.5 mmol gPd−1 min−1). The graphitized carbon black provided the most active catalysts, showing Pd nanoparticles around 3 nm in size and a well-balanced contribution of Pd species (Pdn+/Pd0 = 0.9). Substantial differences of activity were found between the graphitized and not graphitized supports, even for catalysts with similar Pd nanoparticle size. The higher activity of the catalysts with graphitized supports can be partly associated to a more balanced initial Pdn+ to Pd0 ratio. Moreover, higher selectivity to hydrogenation products (cyclohexanone) was also achieved with those catalysts due to a higher contribution of the Pd0 species, The authors greatly appreciate financial support from the Spanish MINECO (CTQ2012-32821)

Adsorption with activated carbons (ACs) has been recently proposed as a thermodynamically favored treatment to remove and/or recover ionic liquids (ILs) from aqueous streams. In this work, a kinetic analysis of the adsorption of a hydrophobic IL (1-methyl-3-octylimidazolium hexafluorophosphate, OmimPF6) by commercial ACs was performed. The results indicated that adsorption kinetics is remarkably slower for the IL than for phenol, used as a reference solute. Then, the effects of the main operating conditions (stirring, AC particle size, temperature, and initial concentration of IL) on the adsorption rate were investigated. For the purpose of developing criteria to improve the kinetics of IL adsorption with ACs, different empirical and phenomenological kinetic models were applied to describe the experimental adsorption data. The kinetic analysis indicated that the mechanism of IL adsorption onto ACs is mainly controlled by the mass transfer into the pores. Therefore, the selection of adequate particle size ...

A wide set of solid carbons obtained by low-density polyethylene (LDPE) pyrolysis has been extensively analyzed by temperature programmed oxidation (TPO) technique. These samples showed different TPO behavior depending on pyrolysis conditions employed, having a wide range of TPO profiles, from one predominant peak to several overlapping curves. The evolution of the oxygen reactivity of LDPE-derived solid carbons heat treated to 1300, 2000, 2300, and 2600 °C was also examined by TPO. The deconvolution of TPO curves of starting and heat-treated carbons allowed the identification of six different peaks consistently occurring in different samples, which was related to groups of carbon domains with equivalent reactivity. Four of them mainly appeared in the starting carbons and were related with more reactive and less ordered carbon domains. The heat-treatment of the carbons allowed the study of the evolution of carbon domain groups from higher to lower oxygen reactivity. A TPO parameter, Tmax has been defined ...

The potential advantages of applying encapsulated ionic liquid (ENIL) to CO

Unsupported Pd nanoparticles of controlled size were tested as catalyst in liquid-phase hydrodechlorination (303–323 K, 1 atm) using 4-chlorophenol (4-CP) as target compound. The Pd nanoparticles were synthesized by chemical reduction, using ethanol and methanol as reducing agents and poly(N-vinyl-2-pyrrolidone) (PVP) as capping agent. The size of the nanoparticles and the Pdn+/Pd0 ratio decreased with increasing alcohol concentration and PVP/Pd ratio, both being lower for ethanol medium. High 4-CP conversion values (80–100%) were achieved at low Pd concentration (2.45 × 10−3 g/ L). Phenol was the only reaction by-product detected in contrast to the previous results with supported Pd catalysts, where the active phase–support interaction in 4-CP HDC led to obtain also cyclohexanone and cyclohexanol as by-products in equivalent experimental conditions. The smaller nanoparticles showed higher activity due to the higher available surface (m2/gcat). Thus, the smaller nanoparticles synthesized in ethanol medium ranged between 2.7 and 2.8 nm and yielded activity values between 16.7 and 39.1 mmol/gcat min, whereas the smaller particles obtained in methanol medium were in the 3.1–4.2 nm range and exhibited activity values of 20.1–25.7 mmol/gcat min. However, the large nanoparticles exhibited higher activity per unit of catalyst surface, for example, 0.34–0.43 mmol/min m2 in the case of those synthesized in methanol medium. On the other hand, higher activity was observed for the nanoparticles synthesized in methanol medium when equivalent nanoparticle size was compared. Activation energy values around 100 kJ/mol were obtained for Pd nanoparticles of different characteristics, significantly higher than the value reported for supported Pd catalysts.

Adsorption with activated carbons (ACs) has been recently reported as an affordable environmental application to remove and recover ionic liquids (ILs) from water streams. In this work, an extensive analysis of the separation of imidazolium-based ILs from aqueous solution, based on adsorption equilibrium experiments at 308 K, has been performed. The study includes five commercial and four modified ACs, with a wide variety of structural and chemical properties, a carbon black and also two inorganic adsorbents. The materials tested were characterized by several techniques in order to establish the role of the porous structure and chemical surface on their adsorption capacities. We found that the microporous ACs with low concentration of polar groups in their surface are the best candidates for adsorption of hydrophobic ILs, reaching uptakes of up to 1 g of IL per gram of adsorbent. The influence of both cation and anion on the adsorption process was analyzed from the adsorption isotherms of 27 different ILs. The dependence of the adsorption uptake with the chemical structure of the ILs was explained by mean of the quantum-chemical COSMO-RS model, which provides information of the intermolecular interactions between the IL adsorbate and the AC adsorbent. As a result, some insight into the adsorbent modifications needed for improving of the adsorption of specific ILs were achieved and successfully applied to the adsorption of hydrophilic ILs by oxidized ACs. In addition, a procedure for regenerating the exhausted adsorbent and recovering the IL by acetone extraction was validated upon successive adsorption–desorption cycles with two commercial ACs. Finally, the acetone was separated by atmospheric distillation, being the IL recovered without structural modification.

We greatly appreciate financial support from the Spanish MCYT (CTQ2009-09983 and CSD2006-44) and CAM (REMTAVARES S-2009/AMB-1588). M. Al Bahri thanks to the Spanish MICINN a research grant (CTQ2006-13512)

The adsorption of diuron from aqueous phase by activated carbon has been analyzed from a molecular point of view thanks to a computational approach based on COSMO-RS methodology, with the aim of providing a mechanistic explanation of the experimental results. The adsorption experiments were carried out at different pH values (3-7) and temperatures (15-45 °C) using an activated carbon prepared by chemical activation of grape seeds. The most relevant characteristics of the adsorption of diuron were the increase of diuron uptake with temperature and the occurrence of multilayer adsorption at high equilibrium concentrations. Likewise, the contribution of cooperative adsorption was also found to increase with temperate, as shown by the change of the isotherm pattern from L-3 type (Giles classification) at 15 °C to S-3 at 45 °C. The formation of multilayer and the contribution of cooperative adsorption were not observed at the highest pH studied The results obtained from the computational approach were consistent with the trends shown by the experimental data. The molecular and thermodynamic properties of the solvent-adsorbate-adsorbent system were estimated using the quantum-chemical COSMO-RS method. Thus, the increase in diuron uptake at increasing temperature was ascribed to a higher population of diuron planar conformers, whose affinity for activated carbon is higher as evaluated in terms of the activated carbon/water partition coefficient. COSMO-RS simulations predicted strong interaction among diuron molecules due to the amphoteric character of the molecule. Likewise, the formation of clusters was found to be especially favored from a thermodynamic point of view in the case of planar conformers adsorbed on activated carbon, which supports the occurrence of cooperative adsorption and the formation of a multilayer, We greatly appreciate financial support from the Spanish MCYT (CTQ2009-09983 and CSD2006-44) and CAM (REMTAVARES S-2009/AMB-1588)

Different commercial and own-made catalysts, synthesized by incipient wetness impregnation, based on Pd and Rh supported on activated carbon have been investigated for hydrodechlorination (HDC) in aqueous phase using 4-chlorophenol as target compound at 100 mg/L starting concentration. The experiments were performed in a continuous stirred basket tank reactor at 30 °C and 1 atm, fairly mild conditions for a potential application to industrial wastewater. Although all the catalysts tested showed a high dechlorination activity (X4-cp ≥ 95% except for the commercial Rh/AC catalyst) which remained practically stable during long-term experiments, the own-made catalysts yielded a higher selectivity (>40%) to the most hydrogenated reaction products, cyclohexanone and cyclohexanol. This last is by far the main reaction product with the own-made Rh catalyst, which is important given its lower toxicity and higher biodegradability. The highest catalytic activity was associated with metal particle sizes within the 3–4 nm range, indicating that the HDC reaction with these catalysts is structure sensitive. Modification of the surface composition of the active carbon support upon HNO3 oxidation entailed a more homogeneous distribution of the active phase with improved metallic dispersion. However, the catalyst with the smallest metal particle (

Supported ionic liquid phase (SILP) materials are a recent concept where a film of ionic liquid (IL) is immobilized on a solid phase, combining the advantages of ILs (non volatility, high solvent capacity, etc.) with those of heterogeneous support materials. In this work, new SILP materials were prepared using a series of supports with different porosity and chemical nature. An imidazolium-based IL, 1-methyl-3-octylimidazolium hexafluorophosphate (OmimPF6), was confined at variable contents (5–60% w/w) in three different activated carbons (ACs), silica (SiO2), alumina (Al2O3) and titania (TiO2). For the first time, a systematic characterization of different SILP systems has been carried out applying a variety of analytical and spectroscopic techniques to provide information of interest on these materials. Elemental analysis (EA), adsorption–desorption isotherms of N2 at 77 K, mercury porosimetry, termogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electronic microscopy (SEM) and energy dispersive X-ray (EDX) were conducted to explore confinement effects. The results demonstrate that EA is a useful tool for quantifying the amount of imidazolium-based IL incorporated on support, independently of the nature of the solid. An excellent correlation has been obtained between the percentage of elemental nitrogen and the IL loaded on the support. The combination of nitrogen adsorption–desorption isotherms at 77 K and mercury porosimetry measurements was used to characterize the pore structure of both supports and SILP materials. It was found that depending on the available pores in the solid support, the IL tends to fill micropores firstly, then mesopores and lately in macropores. Thermal properties of SILP materials were studied herein by using both TGA and DSC methods, evidencing that the stability of SILP materials and the decomposition mechanism are strongly dependent on the surface chemistry of the solid support. SEM and EDX provided evidences of external surface coverage by ILs and filling of macropores at high IL load.

The hydrodechlorination (HDC) of diuron with hydrogen in aqueous phase was studied in a trickle bed reactor using different Pd, Cu and Ni catalysts supported on activated carbon. The reactor was fed with a diuron aqueous solution (2–30 mg/L) and a H 2 /N 2 (1:1) gas stream. Wide ranges of temperature (35–100 °C) and space–time (64.8–647.5 kg cat h/mol) were studied at a pressure of 1.4 bar. HDC of diuron with Pd on activated carbon (Pd/AC) catalyst with 0.5 wt.% Pd can be conducted successfully at 50 °C, reaching conversion values above 95%. The porous structure of the catalysts showed a significant effect on their activity. A nearly complete removal of diuron was achieved with the 0.5 wt.% Pd catalyst of high external (or non-microporous) area, whereas conversion values of around 70% were obtained with the highly microporous catalyst. The resulting effluents showed lower ecotoxicity values than the inlet diuron solution, thus indicating the evolution to less toxic species. Though the Pd catalysts showed a higher activity, the Cu and Ni ones also led to high conversions well above 80% at 2.5 wt.% metal load. Nevertheless, opposite to the Pd catalysts, a significant metal leaching was observed from the Ni and Cu ones, which affected negatively to the ecotoxicity of the final effluents, showing higher values than for the own initial diuron solution. To improve the anchorage of the active phase to the support, activated carbon was subjected to an oxidative treatment with HNO 3 . A significant decrease of leaching was observed, leading to ecotoxicity values comparable to those obtained with the Pd catalysts.

The formation of solid carbons by LDPE pyrolysis has been studied in three different reactors: a batch feed reactor with slow heating (BFRSH), a batch feed reactor with fast heating (BFRFH), and a semicontinuous feed reactor with fast heating (SFRFH). The yield to solid carbons was low in the batch reactors with slow and fast heating (

Low-density polyethylene (LDPE) was pyrolyzed in a quartz semicontinuous feed reactor with fast heating to obtain solid carbons. Two different carbons were obtained by pyrolysis: pyrolytic carbon deposited on the wall of the reactor and spherical carbon from gas-phase nucleation and growth in the inner part of the reactor. The spherical carbon constituted the major portion of the solid carbon product (95%−99%). A two-factorial experimental design was used to study the influence of pyrolysis variables (temperature, nitrogen flow rate, and LDPE feed rate) on morphology, solid carbon yield, and structure. The yield of LDPE to solid carbon was high (15.3%−49.4%) and increased as the temperature and residence time each increased. Solid carbons with more homogeneous morphology and a higher degree of structural order were obtained at higher temperatures as well as lower nitrogen flow rates and lower LDPE feed rates (both leading to a higher residence time of pyrolytic gases).

Catalysts based on pillared clays with Pd-Al were synthesized from a commercial bentonite and tested for catalytic hydrodechlorination (HDC) using 4-chlorophenol (4-CPhOH) as target compound and formic acid as hydrogen source. Stable Pd-Al pillared clays, with a strong fixation of the active phase to the solid support were obtained since no Pd was detected in the reaction media. The incorporation of Pd to the pillared clay structure yielded catalysts with high activity in the reaction studied reaching a complete removal of the 4-CPhOH under mild conditions of temperature (50-70 degrees C). Phenol was not the only reaction product formed, since a more hydrogenated product such as cyclohexanone was detected in the effluent, which indicates additional hydrogenation of phenol. The influence of the method of introduction of Pd in the pillared clay (ion-exchange or impregnation) and Pd concentration in the catalytic activity were studied as well as other important operating variables such as reaction temperature, catalyst concentration, 4-CPhOH initial concentration and formic acid to 4-CPhOH molar ratio. The catalysts prepared suffered deactivation after three consecutive runs, probably due to carboneous deposits formation since no appreciable Pd leaching was observed.

Catalysts based on pillared clays with Al and Pt were synthesized from a commercial bentonite and tested for catalytic hydrodechlorination (HDC) using 4-chlorophenol (4-CPhOH) as the target compound and formic acid as the hydrogen source. Stable Pt–Al pillared clays were obtained, showing a high activity and a strong fixation of the active phase to the support. The influence of the method of introduction of Pt in the pillared clay (ion-exchange or impregnation) and the Pt content in the catalytic activity was checked. Likewise, operating variables such as reaction temperature, catalyst concentration and formic acid to 4-CPhOH molar ratio were studied; higher values of these variables gave rise to a higher 4-CPhOH conversion to phenol. An important deactivation of the catalyst was observed, probably due to the formation of carboneous deposits since no appreciable Pt leaching was detected.

The hydrodechlorination of 4-chlorophenol promoted by different commercial catalysts based on Pd and Rh on γ-alumina and activated carbon has been investigated in a continuous stirred basket reactor (20−40 °C and 1 bar) in order to analyze the kinetics of the reaction. External and internal mass transfer effects were found to be negligible from the values of the Carberry and Weisz−Prater numbers. The reaction rate showed a first-order dependence with respect to 4-chlorophenol. All catalysts were effective in the removal of 4-chlorophenol, with phenol, cyclohexanone, and cyclohexanol identified as reaction products, although the last one was only detected with the Rh/AC catalyst. The highest apparent kinetic constant values correspond to the hydrogenation of 4-chlorophenol to phenol. These values were in the range 146−478 L/kgcat·h for Pd/Al2O3, 179−713 L/kgcat·h for Pd/AC, and 44−172 L/kgcat·h for Rh/AC. The values of the apparent activation energy for 4-chlorophenol disappearance ranged within 47−58 kJ/mol.

This work reports on the feasibility of hydrodechlorination as a treatment technique for chlorophenols-bearing wastewaters using formic acid as a hydrogen source. 4-Chlorophenol (4-CPhOH) has been used as target compound and the experiments were carried out in batch and continuous mode with a commercial activated carbon-supported Pd (0.5 wt.%) catalyst. The variables studied in the batch runs were HCOOH/4-CPhOH molar ratio (10-1000), temperature (25-75 degrees C) and catalyst concentration (250-1000 mg/L). The continuous experiments were performed in a fixed bed reactor where aqueous solutions of formic acid and 4-CPhOH with molar ratios between 50 and 100 were continuously fed to the reactor, at different space-time values in the range of 10.7-42.8 kg(cat)h/mol. Reaction temperatures from 35 to 100 degrees C were tested and the pressure was fixed at 2.5bar. Conversion values above 99% for 4-CPhOH were obtained in batch experiments, but using a HCOOH/4-CPhOH molar ratio as high as 500. Moreover, most of the phenol produced was adsorbed on the catalyst. Continuous runs were performed to evaluate the efficiency of the catalyst under lower HCOOH/4-CPhOH ratios and to explore the possibility of converting phenol to more hydrogenated products. The results indicated that the HCOOH/4-CPhOH molar ratios needed were an order of magnitude lower than those required in batch runs to achieve conversions of 4-CPhOH close to 95%. Besides, phenol was not the only reaction product formed, since a more hydrogenated product such as cyclohexanone was detected in the effluent, which indicates additional hydrogenation of phenol in contrast to the behaviour observed in batch experiments. A loss of activity was observed in the continuous runs after 20-30 h on stream.

The hydrotreatment of crude wax from the dewaxing of spindle, light neutral, medium neutral, heavy neutral, and brightstock oil was studied to obtain refined paraffins that are suitable for high-gr...