Metal‐organic frameworks (MOFs) have emerged as a new class of supports for metal nanoparticles(NPs) in heterogeneous catalysis because of possible synergetic effects between the two components. In ...addition, MOFs also can be coated over metal NPs to influence the entire nanoparticle's surface. Herein, NPs were hybridized with UiO‐66(Hf) MOF possessing Brønsted acidic sites (on secondary building units) and fabricated Pd@UiO‐66 (Hf) core–shell and Pd/UiO‐66(Hf) supported catalysts. These hybrid materials exhibited enhanced catalytic properties (TOF increased up to 2.5 times) compared to individual counterparts or their physical mixture for dehydrogenation of ammonia borane(AB) in non‐aqueous medium(1,4‐dioxane). Further, nanostructure of the hybrid material had pronounced influence on the catalytic properties. The core–shell catalyst exhibited highest activity towards H2 generation from AB owing to greater contact interface between Pd and MOF. Further, phenylacetylene semi‐hydrogenation with AB over Pd@UiO‐66 (Hf) furnished styrene selectivity as high as 93.2 % at ∼100 % conversion mostly due to the regulated phenylacetylene diffusion through UiO‐66(Hf) shell.
Hybridization of Pd nanoparticles with UiO‐66(Hf) improved the catalytic properties remarkably towards ammonia borane dehydrogenation in non‐aqueous medium and phenyl acetylene hydrogenation; the extent and nature of improvements were dependent on the nanostructure of the catalysts.
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•Development of a bioinspired process of template-free synthesis of 1D Bi2S3 nanorods.•Mechanistic exploitation of Bi2S3 nanorods formation mediated by plant-based analyte.•Bi2S3 ...nanorods electrocatalyzed CO2 conversion to HCOO– with high Faradaic efficiency.•Oxidation of Bi2S3-NRs(bio) to Bi2O2CO3, could serve as active sites during ECO2RR.
This work demonstrates a simple bioinspired route of synthesizing template-free 1D Bi2S3 nanorods, Bi2S3-NRs(bio), using Sechium edule fruit. The morphology of nanorods was controlled via capping of ascorbic acid (AA), a major bio-analyte. The average length and diameter were reduced from 485 to 229.5 nm and 123 to 31 nm, respectively, compared with Bi2S3-NRs(control), Bi2S3 nanorods synthesized in the absence of bio-extract/reducing agent. The XPS analysis confirmed that the formation of Bi2O3 in Bi2S3-NRs(control), could be prevented in Bi2S3-NRs(bio) because of AA capping. A plausible mechanistic route of synthesis of Bi2S3-NRs(bio) is also proposed herein. The modified Bi2S3-NRs(bio)/Toray carbon paper (TCP) electrode exhibited selective HCOO– formation with FE of 92.3% against 50.9% for the Bi2S3-NRs(control)/TCP electrode at −1.5 V (vs. Ag/AgCl). Higher FE exhibited by Bi2S3-NRs(bio) catalyst has resulted from its compositional and morphological attributes. In-situ electrochemical oxidation of Bi2S3-NRs(bio) to Bi2O2CO3 also could act as active sites for enhanced and selective HCOO– formation.
Oxidative steam reforming of ethanol (OSRE) was studied over Rh/CeO
2/Al
2O
3 catalysts in a micro-channel reactor. First, the catalyst support, Al
2O
3, was deposited on to the metallic substrate by ...washcoating and then the CeO
2 and active metal were sequentially impregnated. The effect of support composition as well as active metal composition on oxidative steam reforming of ethanol in a micro-channel reactor was studied at atmospheric pressure, with water to ethanol molar ratio of 6 and oxygen to ethanol molar ratio ranging from 0.5 to 1.5, over a temperature range of 350–550 °C. Ceria added to 1%Rh/Al
2O
3 showed higher activity and selectivity than 1%Rh/Al
2O
3 alone. Out of the various catalysts tested, 2%Rh/20%CeO
2/Al
2O
3 performed well in terms of activity, selectivity and stability. The OSRE performance was compared with that of SRE over 2%Rh/20%CeO
2/Al
2O
3 catalyst at identical operating conditions. Compared to SRE, the activity in OSRE was higher; however the selectivity to desired products was slightly lower. The H
2 yield obtained in OSRE was ∼112 m
3 kg
−1 h
−1, as compared to ∼128 m
3 kg
−1 h
−1 in SRE. The stability test performed on 2%Rh/20%CeO
2/Al
2O
3 at 500 °C for OSRE showed that the catalyst was stable for ∼40 h and then started to deactivate slowly. The comparison between packed bed reactor and micro-channel reactor showed that the micro-channel reactor can be used for OSRE to produce hydrogen without any diffusional effects in the catalyst layer.
Steam reforming of ethanol was studied over Rh/CeO2/Al2O3 catalysts in a micro-channel reactor. First, the catalyst support was deposited on to the metallic substrate by washcoating and then the CeO2 ...and active metal were sequentially impregnated. The catalysts were characterized by means of BET surface area, temperature programmed reduction, H2 chemisorption and atomic absorption spectroscopy. The effect of support composition as well as active metal composition on steam reforming of ethanol in micro-channel reactor was studied at atmospheric pressure, with an ethanol to water molar ratio of 1:6, over a temperature range of 400–600°C. Ceria added to 2%Rh/Al2O3 showed higher activity and selectivity than 2%Rh/Al2O3 alone. With addition of Ni to 2%Rh/20%CeO2/Al2O3, the catalyst activity was significantly reduced. Out of the various catalysts tested, 2%Rh/20%CeO2/Al2O3 performed well in terms of activity, selectivity and stability. The micro-channel reactor performance was compared with that of packed bed reactor using 2%Rh/20%CeO2/Al2O3 catalyst at identical operating conditions. The activity was similar in both the reactors but the selectivity to desired products were higher in the micro-channel reactor. The H2 yield obtained in the micro-channel reactor was ∼65Lg−1h−1, as compared to 60LH2g−1h−1 in the packed bed reactor. The stability test performed on 2%Rh/20%CeO2/Al2O3 at 500°C in the micro-channel reactor showed that the catalyst was stable for ∼35h and then started to deactivate slowly.
In the past few years, rising concerns vis-à-vis global climate change and clean energy demand have brought worldwide attention to developing the ‘biomass/organic waste-to-energy’ concept as a ...zero-emission, environment-friendly and sustainable pathway to simultaneously quench the global energy thirst and process diverse biomass/organic waste streams. Bioenergy with carbon capture and storage (BECCS) can be an influential technological route to curb climate change to a significant extent by preventing CO2 discharge. One of the pathways to realize BECCS is via in situ CO2-sorption coupled with a thermal plasma gasification process. In this study, an equilibrium model is developed using RDF as a model compound for plasma assisted CO2-sorption enhanced gasification to evaluate the viability of the proposed process in producing H2 rich syngas. Three different classes of sorbents are investigated namely, a high temperature sorbent (CaO), an intermediate temperature sorbent (Li4SiO4) and a low temperature sorbent (MgO). The distribution of gas species, H2 yield, dry gas yield and LHV are deduced with the varying gasification temperature, reforming temperature, steam-to-feedstock ratio and sorbent-to-feedstock for all three sorbents. Moreover, optimal values of different process variables are predicted. Maximum H2 is noted to be produced at 550 °C for CaO (79 vol%), 500 °C for MgO (29 vol%) and 700 °C (55 vol%) for Li4SiO4 whereas the optimal SOR/F ratios are found to be 1.5 for CaO, 1.0 for MgO and 2.5 for Li4SiO4. The results obtained in the study are promising to employ plasma assisted CO2-sorption enhanced gasification as an efficacious pathway to produce clean energy and thus achieve carbon neutrality.
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•Development of 2D spinel Co3O4 nanodiscs (NDs) in a bioinspired route.•Mechanistic exploitation of 2D Co3O4 NDs formation by gallic acid.•Co3O4 NDs electrocatalyzed N2 reduction to ...NH3.•Co3O4 NDs facilitated electron transfer for N2 reduction reaction.•6-fold higher Faradaic efficiency of NH3 formation over bare carbon paper.
The production of ammonia through electrochemical nitrogen reduction reaction (ENRR) has garnered significant interest as a potential method of artificial nitrogen fixation in ambient conditions. This study reports an environmentally friendly synthesis of pristine Co3O4 nanodiscs (NDs) as a catalyst to effectuate electrochemical nitrogen reduction to ammonia. The absorption spectra of Co3O4 NDs revealed two peaks at 435 and 735 nm, indicative of O2− to Co2+/Co3+ charge transfer. The particles exhibited a distinct propensity for the growth along the (311) direction with induced oxygen vacancies which resulted from the release of NOx from the decomposition of precursor in the calcination step. The diameter and thickness of Co3O4 NDs were determined to be 240 and 35.5 nm, respectively. Faradaic efficiency of NH3 production of 2.6% was achieved with a yield rate of 8.8 µg h−1 mgcat.−1 at −1.25 V (vs. Ag/AgCl). Co3O4 NDs/TCP electrode showed six times higher Faradaic efficiency (FE) for ENRR compared to the bare TCP electrode. However, prolong electrolysis could result a reduction in FE due to sacrifice of active Co(III) sites due to the formation of Co(OH)2. Co2+ in tetrahedral sites easily bond with the N≡N, whereas Co3+ in octahedral sites facilitate the electron transfer for ENRR.
In the present study, the effect of primer and slurry composition on the washcoat characteristics of γ-alumina on stainless steel substrate has been investigated. Washcoating was done following a ...two-step procedure: primer coating followed by slurry coating. Washcoat was characterized by SEM, adherence test and BET surface area measurement. For coating of the primer, Disperal with or without polyvinyl alcohol (PVA) was used. Without PVA, the sol settled in the microchannels whereas at high concentrations of PVA, the sol was too viscous. The optimum primer composition was found to be 2% Disperal and 4% PVA. In the subsequent slurry coating step, various properties of the slurry such as pH, viscosity, solid loading were optimized to obtain well-adhered, uniform washcoat on stainless steel substrate. PVA was added to the slurry to increase the binding and also enhance the viscosity, resulting in better adherence. An adverse effect of adding PVA was a reduction in the surface area. To reduce the amount of PVA and thereby its adverse effect, other binders (colloidal alumina and Disperal) were evaluated. Uniform well-adhered washcoats were obtained with particle size of γ-alumina less than 3
μm, and slurry composition: 14
wt.% γ-alumina, 2
wt.% PVA, 6
wt.% colloidal alumina and remaining water. Finally, the best washcoat obtained in this study was impregnated with 2% Rh–5% Ni and tested in the steam reforming of ethanol. For comparison, runs were also taken on powdered catalysts in a packed bed reactor at identical conditions and the conversions obtained in both the reactors were similar.
The kinetics of steam reforming of ethanol (SRE) was determined at atmospheric pressure in the temperature range of 450–550 °C over 2% Rh/20% CeO2/Al2O3 in a microchannel reactor. The product ...distribution could be explained by a reaction scheme consisting of four reactions: reaction of steam with ethanol, decomposition of ethanol, methane steam reforming, and the water-gas shift reaction. The kinetic expression based on Langmuir–Hinshelwood kinetics could explain the experimental data satisfactorily. A two-dimensional simulation was also carried out to predict the performance of a microchannel SRE reactor in which the endothermic heat of reaction was supplied by the co-current flow of a hot gas in the adjacent channel. The performance of the coupled reactor/heat exchange system was evaluated by varying several parameters such as heating side gas velocity and temperature, width of the channel, weight of the catalyst, reactor inlet temperature, and inlet flow rate.
The development of efficient metal doped semiconductors for solar energy harvesting to produce hydrogen has attracted significant attention. Herein, the H2 generation over Ag-doped TiO2 ...photocatalyst, synthesized using a simple and cost-effective method based on chemical reduction, was reported. The Ag/TiO2 exhibited an absorption peak in the visible region and the reduction of the bandgap to 2.5 eV due to surface plasmonic resonance (SPR). X-ray photoelectron spectroscopy revealed the presence of oxygen vacancies and 11% of Ag in Ti–Ag–O phase. The effect of reaction time and photocatalyst loading in the absence and presence of sacrificial reagents (alcohols and sulfur) on water splitting was studied and compared the activity of Ag/TiO2 with that of bare TiO2. The H2 production rate of 23.5 mmol g−1 h−1 (with an apparent quantum yield of 19%), over 1.5Ag/TiO2, was the highest ever reported so far. The observed higher activity could mainly be attributed to the existence of oxygen vacancies and the Ti–Ag–O phase. The photocatalyst was stable for three consecutive cycles in both the presence and absence of sacrificial reagents. This study offers new insights into the rational design of metal-support hybrid structures for hydrogen production through photocatalytic water splitting.
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•The Ag/TiO2 synthesized by chemical reduction, lowers the band gap of TiO2.•XPS confirms oxygen vacancies and Ag in both Ag0 and Ti–Ag–O phases.•The Ti–Ag–O phase promotes efficient charge transfer and separation.•Oxygen vacancies and Ti–Ag–O in Ag/TiO2 enhances the photoreduction of water to H2.•Remarkable H2 production of 23.5 mmol g−1 h−1 over Ag doped TiO2.
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•Ru-V2O5/AC (activated carbon) bimetallic catalysts were successfully synthesized.•Glycerol to lactic acid: Ru-V2O5/AC outperformed their monometallic counter parts.•75.5% lactic acid ...yield was achieved at 98.7% glycerol conversion over Ru-V2O5/AC.•The Ru-V2O5/AC bimetallic catalysts exhibited synergism between Ru and V2O5.•The Ru-V2O5/AC catalysts exhibited excellent stability for up to four cycles.
Ongoing trends to increase biodiesel production translates into enhanced surplus glycerol production, driving the need to develop value-added products, such as lactic acid, from glycerol. The present work is devoted to synthesizing Ru-V bimetallic and monometallic catalysts supported on activated carbon and testing them to produce lactic acid from glycerol through selective aerobic oxidation. The synthesized catalysts were thoroughly characterized to obtain morphological and structural properties, elemental composition, and surface area. The Ru-V2O5/AC (Ru-V/AC) bimetallic catalysts demonstrated superior performance to monometallic Ru and V catalysts, exhibiting a synergistic effect. The Ru-V/AC bimetallic catalyst containing 1.5 wt% Ru and 0.5 wt% V exhibited the best catalytic performance with a lactic acid yield of 75.5% at 98.7% glycerol conversion under mild operating conditions (1 NaOH/glycerol molar ratio, 4400 glycerol/metal molar ratio, 473 K temperature, 5 Bar air pressure and 3 h reaction time). The Ru-V/AC bimetallic catalyst showed good stability during the reaction with only a marginal loss in activity when reused for four consecutive cycles, suggesting that this catalyst can be recycled multiple times.
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