Exceptional performance of gold supported on fluoridated hydroxyapatite catalysts in CO-cleanup of H2-rich stream: High activity and resistance under PEMFC operation conditions

Proton-exchange-membrane fuel cells (PEMFCs) appear to be the most promising solution for future automotive applications. Facing the lack of efficient hydrogen storage and transportation solutions, current research is focused on the development of on-board catalytic reformers. In this strategy, the purity of hydrogen stream is still an unresolved issue that needs to be addressed in order to avoid poisoning of the Pt electrodes of PEMFC. Here we report the extraordinary performance of gold supported on fluorine-substituted hydroxyapatite (HAP) catalysts in the CO preferential oxidation (COPROX) process. At 80 ◦C, the optimized catalyst (Au/F-(1)) proves to be highly active, selective (showing a CO conversion (XCO) of 100 % and selectivity towards CO2 production (SCO2) close to 62 %) and very resistant to deactivation, even in the presence of H2O (15 %) and CO2 (20 %). In addition, these results were obtained at relatively high weight hourly space velocity (WHSV: 60,000 cm3 g-1 h-1). It should be highlighted that our catalysts clearly outperform state-of-the-art gold catalysts. Our discovery introduces Au/F(x)-HAP catalysts as a viable solution for an effective elimination of CO to feed PEMFCs with CO-free hydrogen streams.The financial support for this work provided by Ministerio de Economía y Competitividad (CTQ2015-73219-JIN (AEI/FEDER/UE) and ENE2016-74850-R) and Basque Government (GIC IT-1297-19) is gratefully acknowledged

Viability of Au/La2O3/HAP catalysts for the CO preferential oxidation reaction under reformate gas conditions

The viability of gold supported on lanthanum-modified HAP catalysts is investigated for CO preferential oxidation (PROX) in H-2-rich stream. All samples comprise small nanoparticles (NPs) of Au (< 4 nm). Addition of La enhances the chemisorption of CO, whereas it lowers that of H-2 and H2O. Moreover, lanthanum improves the reducibility of the catalysts and the mobility of oxygen. FTIR studies show that under CO oxidation conditions Au exists in two distinct forms on La-promoted samples, namely Au sigma+ and Au+ species. The catalytic tests under different PROX conditions show an improvement of the performance with lanthanum addition. The observed improvement is linked to suitable chemical properties, whereas efficiency dependence on Au NP sizes is rather secondary. At 80 degrees C, La-rich catalysts completely eliminate CO and prove to be selective (66%) under realistic PROX conditions (in the presence of H2O and CO2). Moreover, they are exceptionally stable during an extended period (240 h).The financial support from the Basque Government (IT1509-22) is acknowledged. The authors also acknowledge the technical support provided by SGIker (UPV/EHU Advanced Research Facilities/ERDF, EU)

Effect of the synthesis method on the performance of Ni-CeO2-ZrO2 catalysts for the hydrogenolysis of glycerol with endogenous hydrogen

In this work, we investigated the influence of the synthesis method of Ni-based CeZr catalysts on their physicochemical and catalytic properties in the hydrogenolysis (HDO) of glycerol with H2 in-situ produced by the aqueous-phase reforming (APR). Conventional impregnation method involved surface nickel deposition (NiCeZr-IM). The one-pot methods, which involved nickel embedment into CeZr lattice, included sol-gel (NiCeZr-SC) and coprecipitation (NiCeZr-CA and ultrasound-assisted NiCeZR-CS) methods. Differences in textural, structural, morphological, redox, and surface properties, together with and catalytic performance in the glycerol APR-HDO, were investigated systematically. As well, spent catalysts were deeply characterized. There were notable differences among textural properties, which significantly affected their activity in glycerol conversion. The structural characterization confirmed the successful integration of Ni into the CeZr lattice, especially for the catalysts synthesized using one-pot methods. One-pot synthesized catalysts showed stronger Ni-CeZr interaction, which affect the reducibility. The catalysts prepared by coprecipitation contained the highest metal-to-acid ratio, making them very active for C-O bond hydrogenation. Post-reaction characterization discloses a leaching of the nickel, in greater amount for both coprecipitated catalysts. This study revealed the potential of Ni-based catalysts derived from subsurface insertion of nickel into the CeZr matrix for the hydrogenolysis of glycerol without external hydrogen.Ministerio de Ciencia e Innovación, PID2019-106692RB-I0

Nickel aluminate spinel-derived catalysts for the aqueous phase reforming of glycerol: Effect of reduction temperature

Bulk nickel aluminate (NiAl2O4) was synthesised by co-precipitation at a Ni/Al mole ratio of 1:2 (stoichiometric ratio). The prepared sample was reduced at different temperatures, in the 300 to 850 ºC range, and obtained assays were analysed by a wide range of analytical techniques (XFR, XRD, H2-chemisoprtion, H2-TPR, DRS UV-vis NIR, FTIR, 27Al MAS NMR, NH3-TPD, CO2-TPD, TPO) and tested for the APR of glycerol. The spinel precursor allowed the formation of small and stable Ni particles (< 14 nm) upon reduction with good performance in the APR of glycerol (NiAl-850 93% conversion, 57% conversion to gas, at 250 ºC/45 bar and WHSV 24.5 h-1). Hydrogen was the main gaseous product and the activation temperature did not substantially alter selectivity to gaseous products; however, selectivity to intermediate oxygenated liquid compounds was substantially modified. Overall, glycerol dehydrogenation route was dominant at high reduction temperature. The good stability of the spinel led to stable H2 yield in the long-term runs (50 hours) and proved potential to be used in the APR of glycerol.Ministerio de Economía y Competitividad, ENE2016-7450-

Aqueous-Phase Glycerol Conversion over Ni-Based Catalysts Synthesized by Nanocasting

[EN] A morphological strategy consisting of nanocasting synthesis of nickel aluminate spinel precursor was addressed. Two nanocasted catalysts were synthesized involving different template-removal procedures (i.e., Teflon-assisted calcination vs. NaOH washing) for spinel recovery. As a reference, spinel NiAl2O4 supported by SBA-15 and bare nickel aluminate spinel were selected. The obtained solids were characterized in detail, examining their textural, acid–base, structural and compositional characteristics, either in the calcined or reduced forms. The as-obtained catalysts’ performance was evaluated in the aqueous-phase reforming of glycerol at 235 °C and 35 bar. Exhausted samples were also characterized to enlighten changes in catalyst properties during the aqueous-phase reaction. NiAl/SBA-15 and NiAl-NCF catalyst showed very poor catalytic performance for the glycerol transformation. NiAl-NCN catalyst presented improved activity with respect to NiAl, with a 20% higher hydrogen production rate but, as a drawback, higher methane formation for a whole range of glycerol conversions. Exhausted catalyst indicated nickel oxidized in liquid phase reaction.This research was supported by grant PID2019-106692EB-I00 funded by MCIN/AEI/ 10.13039/501100011033

Bimetallic Pt-Co Catalysts for the Liquid-Phase WGS

[EN] Bimetallic Pt-Co catalysts derived from cobalt aluminate spinel were investigated in the liquid-phase water–gas shift (WGS) reaction and CO hydrogenation. Liquid-phase WGS is a key reaction in the aqueous-phase reforming (APR) of polyols; thus, WGS activity is essential to formulate good APR catalysts. In this work, catalysts with different Pt/Co molar ratios were synthesized together with a reference Pt/alumina. All the synthesized catalysts were characterized by various techniques in order to gain knowledge on their structural and surface characteristics. WGS activity was tested with a feedstream of CO/H2O = 1/15 (space-time of 76.8 kg·s/molCO), isothermal operation at 260 ºC and 50 bar, for 10 TOS. Bimetallic Pt-Co catalysts showed improved activity in liquid-phase WGS in comparison to bare Co or Pt catalysts, which was ascribed to the synergistic effect. Despite being subjected to an increased hydrogen concentration in the feedstream (H2/CO between 0 and 12/3), these catalysts maintained a preferential selectivity towards WGS activity. In addition, the effect of temperature (220–260 ºC) and pressure (25–50 bar) was investigated over a catalyst with 0.3Pt/CoAl. CO conversion and CO2 yield were more sensitive to temperature, while a higher pressure favored methane production. The measured activation energy in the 220–260 ºC temperature range was 51.5 kJ/mol.This research was funded by Mineco (ENE2016-74850-R and PID2019-106692EB-I00) and FEDER. The APC was funded by ENE2016-74850-R. A.J.R. was supported by a PhD research fellowship provided by the University of the Basque Country UPV/EHU (PIF-17/319)

Bio‑hydrogen and valuable chemicals from industrial waste glycerol via catalytic aqueous-phase transformation

Waste glycerol obtained as by-product of biodiesel production has been submitted to a sequential physico-chemical treatment in order to make it suitable for continuous Aqueous-Phase Reforming (APR) in a tubular reactor. Special focus was given to the impact of impurities. APR was performed using 0.3%Pt/CoAl2O4 catalyst, at 260 °C and 50 bar within WHSV range 6–55 h−1 to cover whole conversion ranges. Glycerol conversion and yield to hydrogen reached 99.7% and 45.4%, respectively at WHSV = 6 h−1. The liquid product distribution strongly varied with glycerol conversion, maximum C-yield to 1,2-propylene glycol was attained in the 60–90% glycerol conversion range. APR of methanol and acetic acid aqueous feedstreams were investigated independently. It was concluded that acetic acid exerts a negative influence on catalyst stability since glycerol conversion decreased by 41% after 5 h TOS. Extensive characterization of fresh and exhausted catalysts revealed strong Co leaching, especially for acetic acid APR, oxidation of metals, and carbonaceous deposits. The basis for the regeneration of the spent catalyst, consisting of a reductive treatment at 500 °C, has been established. This work is expected to have significant implications for the development of APR technology for crude glycerol from biodiesel industry.This research was supported by grant PID2019-106692EB-I00 funded by MCIN/AEI/10.13039/501100011033. The authors thank for technical support provided by SGIker of UPV/EHU and European funding (ERDF and ESF)

Aqueous-phase reforming of glycerol over Pt-Co catalyst: Effect of process variables

This study examined the influence of process variables (glycerol concentration in feed, coupled temperature/pressure and space velocity) in the catalytic performance in the APR of glycerol over 0.3Pt/CoAl catalyst in a continuous fixed-bed reactor in order to maximize the production of H2. The effect of glycerol concentration in the feed was studied from 5 to 20 wt%, the coupled temperature/pressure varied from 225 °C/25 bar to 260 °C/50 bar and the spatial velocity was changed from 0.68 to 17 h-1. Our results reflected that H2 production was favored at higher reaction temperature/pressure (3.62 vs. 2.49 molH2/molGly-converted, at the most severe and mild conditions, respectively), lower WHSV (3.89 vs. 1.27 molH2/molGly-converted, at the lowest and highest space velocity, respectively) and more diluted feedstocks (3.95 vs. 1.44 molH2/molGly-converted, at the most diluted and concentrated freestreams, respectively). A threshold value at 10 wt% glycerol was found for the ratio of dehydrogenation to dehydration liquid products. The post-reaction catalyst was also characterized by several techniques, showing that Co leaching was the major drawback, especially at the mildest operation conditions, while carbonaceous deposits are negligible.Ministerio de Ciencia e Innovación, PID2019-106692RB-I0

Cobalt aluminate spinel-derived catalysts for glycerol aqueous phase reforming

Catalytic activity at mild (235 °C/3.5 MPa) and severe (260 °C/5.0 MPa) APR conditions was investigated over catalysts based on cobalt aluminate spinel synthetized by coprecipitation. Co/Al ratio was varied and physicochemical characteristics were assessed by N2 adsorption, H2 chemisorption, XRD, H2-TPR, DRS-UV, FTIR, CO2-TPD, NH3-TPD and XPS. Formation of cobalt aluminate produced strong Co-O-Al interaction in the catalyst precursor leading to improved Co dispersion upon activation. Co/Al ratio could be used to tune catalyst characteristics, thus selectivity towards the desired reaction pathway. Overall, Co/Al above the stoichiometric value produced smaller and more stable metallic Co, which allowed best APR performance. For instance, at 235 °C/3.5 MPa glycerol conversion and conversion to gas of 0.625CoAl (88% and 22%) were notably higher than those of bare Co3O4 (23% and 5%). At severe conditions, 0.625CoAl catalyst produced 231 μmolH2/gcat min (60% H2). Statistical analysis of data collected from long-term run was used to investigate reaction mechanism. Long-term run revealed that sintering and oxidation were main mechanisms for catalyst deactivation whereas some leaching of Co nanoparticles, and carbonaceous deposition was also detected.Ministerio de Economía y Competitividad, ENE2016-7450-

A Preliminary Study on the Use of Highly Aromatic Pyrolysis Oils Coming from Plastic Waste as Alternative Liquid Fuels

In this work, the low-temperature pyrolysis of a real plastic mixture sample collected at a WEEE-authorised recycling facility has been investigated. The sample was pyrolysed in a batch reactor in different temperature and residence time conditions and auto-generated pressure by following a factorial design, with the objective of maximising the liquid (oil) fraction. Furthermore, the main polymers constituting the real sample were also pyrolysed in order to understand their role in the generation of oil. The pyrolysis oils were characterised and compared with commercial fuel oil number 6. The results showed that in comparison to commercial fuel oil, pyrolysis oils coming from WEEE plastic waste had similar heating values, were lighter and less viscous and presented similar toxicity profiles in fumes of combustion.This research was funded by the Department of Economic Development and Infrastructures of The Basque Government through its ELKARTEK 2023 Program (NEOPLAST 2 Project, Reference KK-2023/00060), and also by CDTI (Centro para el Desarrollo Tecnológico Industrial), within the framework of grants for Technological Centers of Excellence “Cervera” (OSIRIS Project, CER-20211009)