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The hydrogenation of CO2 is a reaction of key technological and environmental importance, as it contributes to the sustainable production of fuels while assisting in the reduction of a major greenhouse gas. The reaction has received substantial attention over the years within the catalysis and electrocatalysis communities. In this respect, the electrochemical promotion of catalysis (EPOC) has been applied successfully to the CO2 hydrogenation reaction to improve the catalytic activity and selectivity of conductive films supported on solid electrolytes. However, designing an effective electrocatalytic reactor remains a challenge due to the connections required between the electrodes and the external potentiostat/galvanostat. This drawback could be alleviated if the catalytic reaction occurs in a reactor that simultaneously operates as a power generator. In this work, the Electrochemical Promotion of the CO2 hydrogenation reaction in a low-temperature solid oxide electrolyte fuel cell (SOFC) reactor is studied using yttria-stabilized zirconia (YSZ) and a platinum (Pt) electrode catalyst. The system has been studied in two distinct operation modes: (i) when the necessary energy for the electrochemical promotion is produced through the parallel reaction of H2 oxidation (galvanic operation) and (ii) when a galvanostat/potentiostat is used to impose the necessary potential (electrolytic operation). The performance of the fuel cell declines less than 15% in the presence of the reactant mixture (CO2 and H2) while producing enough current to conduct EPOC experiments. During the electrolytic operation of the electrochemical cell, the CO production rate is significantly increased by up to 50%.

Electrochemical promotion was used to modify the activity and selectivity of a Rh catalyst electrode in the CO2 hydrogenation reaction. The experiments were carried out in a temperature range of 350–430 °C at ambient pressure and at different CO2 to H2 gas feeding ratios (1:2 to 4:1). The only reaction products observed were CO and CH4, both under open- and closed-circuit conditions. The CH4 formation rate was found to increase with both positive and negative potential or current application. The CO formation rate followed the opposite trend. The selectivity to CH4 increased under high values of hydrogen partial pressure and decreased at high pressures of CO2. The results demonstrate how electrochemical promotion can be used to finely tune activity and selectivity for a reaction of high technical and environmental importance.

Transition metal oxides are promising candidates for the activation of the reverse water gas shift (RWGS) reaction.

The electrochemical promotion of catalytic activity by non-noble transition metals is rarely reported in the literature. Here, Co nanoparticles were utilized for the electrochemical activation of C...

The reactivity of furfural with metal surfaces, including Pt(111), has been the subject of various investigations owing to its importance in heterogeneously catalyzed biomass upgrading processes. T...

Herein, for the first time, we demonstrate a novel continuous flow process involving the application of tetralin as a hydrogen donor solvent for the catalytic conversion of oleic acid to diesel-like hydrocarbons, using an efficient and stable carbon-supported bimetallic PdCu catalyst. Using Pd60Cu40/C, where 60 : 40 is the molar ratio of each metal, at optimum reaction conditions (360 °C and WHSV = 1 h−1), 90.5% oleic acid conversion and 80.5% selectivity to C17 and C18 paraffinic hydrocarbons were achieved. Furthermore, a comprehensive mechanistic based kinetic modelling – considering power rate law, L–H and E–R models was conducted. Kinetic expressions derived from the three kinetic models were investigated in rate data fitting through nonlinear regression using a Levenberg–Marquardt algorithm. Based on the statistical discrimination criteria, the experimental data of the dehydrogenation reaction of tetralin were best fitted by an L–H rate equation assuming the surface reaction as the rate controlling step. In contrast, the kinetic data of the oleic acid deoxygenation reaction were well correlated with an L–H rate equation assuming single site adsorption of oleic acid with dissociative H2 adsorption. It was found that the rate limiting step of the overall reaction was the hydrogenation of oleic acid with an activation energy of 75.0 ± 5.1 kJ mol−1 whereas the dehydrogenation of tetralin had a lower activation energy of 66.4 ± 2.7 kJ mol−1.

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In the present study, an inexpensive and practical way to detect phenolic compounds in wastewater was investigated. By using a simple one compartment three-electrode cell and performing cyclic voltammetry measurements, it was possible to quantitatively determine the presence of gallic and vanillic acid in acidic aqueous solutions due to their electrooxidation upon potential scanning. In the case of gallic acid, two oxidation peaks were observed whereas the vanillic acid cyclic voltammograms consisted of two oxidation and one reduction peaks. Correlation of the observed electrooxidation current density value with the concentration of each phenolic compound led to a linear relationship. Following the above methodology for a 1:1 mixture of these phenols, it was found that only a qualitative analysis was possible rather than a quantitative one.

This work reported a new strategy in producing synthetic diesel hydrocarbons from a mono-unsaturated fatty acid model compound, oleic acid and replacing high pressure molecular hydrogen with a hydrogen-rich donor solvent, 1,2,3,4–tetrahydronaphthalene for the first time. Under the absence of an external H2 supply, oleic acid was dispersed in 1,2,3,4-tetrahydronaphthalene and hydrotreated over commercially available 5 wt% Pd/C in a fed-batch reactor to obtain diesel range fuel products. A maximum oleic acid conversion of 92.4% and highest diesel hydrocarbon selectivity of 67.4% were achieved at 330 °C with a solvent to fatty acid mass ratio of 1 for 3 h under autogenous pressure. In-situ H2 produced from 1,2,3,4-tetrahydronaphthalene operated as an effective hydrogen donor vehicle that continuously transported active hydrogen species from gas phase to reactant acid molecules and radical fragments. It minimized polymerization of reaction intermediate and suppressed coke formation, which subsequently improved catalyst resistance toward deactivation.

The catalytic cracking of polyolefinic waste materials over solid acid catalysts, such as zeolites, is a promising process for the production of useful fuels and chemicals. However, the inherent diffusional constraints of the microporous zeolites restrict the access of bulky polyolefin molecules to the active site, therefore limiting their effectiveness. To address this, a simple yet effective method of producing mesoporous Al-SBA-15 materials with a high density of Brønsted acid sites has been employed. These catalysts are shown to be very active for the catalytic cracking of low density polyethylene (LDPE), a common waste plastic. The acidic and textural properties of the catalysts were characterised by ICP-OES, XPS, XRD, N2 physisorption, propylamine-TPD, pyridine-FTIR and STEM and have been correlated with their catalytic activity. The product distribution from the catalytic cracking of LDPE has been shown to depend strongly on both the pore architecture and the Al content of the SBA-15 and thus the density and strength of Brønsted acid sites. Fine-tuning the Al content of the SBA-15 materials can direct the product distribution of the hydrocarbons. The Al-SBA-15 materials display increased cracking orientated towards aliphatic hydrocarbons compared to ZSM-5, attributed to the mesoporous nature of SBA-15, overcoming diffusional limitations.

A range of Pt:Cu bimetallic nanoparticles were investigated for the liquid-phase selective hydrogenation of furfural, an important platform biomass feedstock. Alloying of the two metals had a profound effect on the overall catalytic activity, providing superior rates of reaction and achieving the needed high selectivity towards furfuryl alcohol. Furthermore, we investigated the catalytic activity of an Ultra Dilute Alloy (UDA) formed via the galvanic replacement of Cu atoms by Pt atoms on dispersed host Cu nanoparticles (atomic ratio Pt:Cu 1:20). This UDA, after overcoming an induction period, exhibits exceptionally high initial rates of hydrogenation under modest hydrogen pressures of 10 and 20 bar, rivalling the catalytic turnover for the monometallic Pt (containing 12 times more Pt), and outdoing the pure Cu or other compositions of bimetallic nanoparticle alloy catalysts. These atom efficient catalysts are ideal candidates for the valorization of furfural due to their activity and vastly greater economic viability.

Bimetallic PdxNi(100-x) and PdxCu(100-x) structures of a wide compositional range supported on activated carbon were synthesised via a simple, cheap and commercially relevant method. The surface and bulk properties of both the bimetallic structures and their monometallic counterparts were determined via STEM-EDS, TEM, XPS, powder XRD, N2 porosimetry and ICP-OES. A close correlation between the XRD patterns and EDS elemental composition mapping of individual metal particles established the extent of palladium-base metal interaction in each sample. The performance of the different structures as catalysts for the selective hydrogenation and hydrodeoxygenation of oleic acid, a prototypical fatty acid, was evaluated using tetralin as a hydrogen donor. Catalysts displaying true bimetallic/alloy formation were found to improve the conversion of tetralin as compared to catalysts in which compositional segregation was observed. The PdxNi(100-x) series was found to outperform the PdxCu(100-x) catalysts in terms of hydrogen production via the dehydrogenation of tetralin, mirroring the fact that compositional segregation occurs more for the PdxCu(100-x) series than PdxNi(100-x). The hydrogen transfer deoxygenation of oleic acid over the monometallic and bimetallic catalysts was found to mirror the availability of hydrogen with those catalysts liberating more hydrogen also favouring the formation of C17 and C18 alkanes.

The majority of the kinetic studies reported in the literature for heterogeneously catalyzed reactions, take place on laboratory scale reactors. In the present study, the kinetic mechanism of electrochemical promotion of CO2 hydrogenation was investigated using a scaled up, monolithic electropromoted reactor (MEPR) loaded with nine parallelly connected Ru/YSZ/Au electrochemical cells. The study was carried out under atmospheric pressure, at 370 °C, with a flowrate of 1000 cm3/min and over a wide range of reactants partial pressures. The morphological and electronic characteristics of the catalyst surface, before and after reaction, were thoroughly investigated with a variety of techniques including X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD). It was shown that increasing the partial pressure of H2 (electron donor) leads to an increase in the methane production rate with a concurrent decrease of CO formation. Methanation emerges with a positive order in H2 whereas the RWGS with a negative one. Increasing the partial pressure of electron acceptor (CO2) leads to the opposite behavior. Based on the kinetic results and the rules of chemical and electrochemical promotion, an electrophobic behavior (increase of the rate with increasing catalyst potential) is expected for the methanation reaction and an electrophilic (decrease of the rate with increasing catalyst potential) for the RWGS reaction. Both predictions are confirmed experimentally. The results are in agreement with previous studies on CO2 hydrogenation in laboratory scale reactors demonstrating the successful design and operation of the current scaled up electropromoted system (MEPR).

Lipase immobilised on silica monoliths has been prepared and applied as biocatalytic continuous-flow microreactors for the transesterification of tributyrin as a model bio-oil component. Candida antarctica lipase was trapped within the pores of silica monoliths, and its successful immobilisation was demonstrated by the hydrolysis of 4-nitrophenyl butyrate to 4-nitrophenol. Lipase immobilised on silica monoliths was active for the transesterification of tributyrin at ambient temperature, with reactivity as a function of the methanol : tributyrin ratio, flow rate, temperature, and textural properties. Monoliths with a high surface area and large meso- and macropore channels enhanced the transesterification activity through improved molecule diffusion. The optimum immobilised lipase microreactor exhibited almost quantitative ester production for >100 h at 30 °C without deactivation.

Single-atom catalysts serve as a skilful control of precious metals on heterogenous catalysts where all active sites are accessible for catalytic reactions. Here we report the adoption of PdCu single-atom alloys supported on alumina for the selective hydrogenation of furfural. This is a special class of an atom efficient, single-site catalyst where trace concentrations of Pd atoms (0.0067 wt%) displace surface Cu sites on the host nanoparticle. Confirmed by EXAFS, the Pd atoms are entirely coordinated to Cu, with Pd-Cu bond lengths identical to that of a Cu-Cu bond. Selectively surface oxidised catalysts also confirm surface Pd atoms by EXAFS. These catalysts improve the conversion of furfural to furfuryl alcohol compared to monometallic catalysts, as they have the advantages of Cu (high selectivity but poor activity) and Pd catalysts (superior activity but unselective) without the drawbacks, making them the optimal catalysts for green/atom efficient catalysis.

Furfural is a key bioderived platform chemical whose reactivity under hydrogen atmospheres affords diverse chemical intermediates. Here, temperature-programmed reaction spectrometry and complementary scanning tunneling microscopy (STM) are employed to investigate furfural adsorption and reactivity over a Pt(111) model catalyst. Furfural decarbonylation to furan is highly sensitive to reaction conditions, in particular, surface crowding and associated changes in the adsorption geometry: furfural adopts a planar geometry on clean Pt(111) at low coverage, tilting at higher coverage to form a densely packed furfural adlayer. This switch in adsorption geometry strongly influences product selectivity. STM reveals the formation of hydrogen-bonded networks for planar furfural, which favor decarbonylation on clean Pt(111) and hydrogenolysis in the presence of coadsorbed hydrogen. Preadsorbed hydrogen promotes furfural hydrogenation to furfuryl alcohol and its subsequent hydrogenolysis to methyl furan, while suppressing residual surface carbon. Furfural chemistry over Pt is markedly different from that over Pd, with weaker adsorption over the former affording a simpler product distribution than the latter; Pd catalyzes a wider range of chemistry, including ring-opening to form propene. Insight into the role of molecular orientation in controlling product selectivity will guide the design and operation of more selective and stable Pt catalysts for furfural hydrogenation.

The catalytic and structural properties of five different nanoparticle catalysts with varying Au/Ni composition were studied by six different methods, including in situ X-ray absorption spectroscopy and density functional theory (DFT) calculations. The as-prepared materials contained substantial amounts of residual capping agent arising from the commonly used synthetic procedure. Thorough removal of this material by oxidation was essential for the acquisition of valid catalytic data. All catalysts were highly selective toward N2 formation, with 50–50 Au:Ni material being best of all. In situ X-ray absorption near edge structure spectroscopy showed that although Au acted to moderate the oxidation state of Ni, there was no clear correlation between catalytic activity and nickel oxidation state. However, in situ extended X-ray absorption fine structure spectroscopy showed a good correlation between Au–Ni coordination number (highest for Ni50Au50) and catalytic activity. Importantly, these measurements also demonstrated substantial and reversible Au/Ni intermixing as a function of temperature between 550 °C (reaction temperature) and 150 °C, underlining the importance of in situ methods to the correct interpretation of reaction data. DFT calculations on smooth, stepped, monometallic and bimetallic surfaces showed that N + N recombination rather than NO dissociation was always rate-determining and that the activation barrier to recombination reaction decreased with increased Au content, thus accounting for the experimental observations. Across the entire composition range, the oxidation state of Ni did not correlate with activity, in disagreement with earlier work, and theory showed that NiO itself should be catalytically inert. Au–Ni interactions were of paramount importance in promoting N + N recombination, the rate-limiting step. España, MINECO under Project CTQ2015-64669-P European Union FEDER Program and MINECO under Project CTQ2014-60524-R and ENE2017-88818-C2-1-R

Biochar catalysts exhibit significant activity and stability, for the activation of sodium persulfate (SPS) and consequently the oxidation of organic contaminants. In this study, the influence of SPS on the physicochemical characteristics and catalytic activity of biochar was determined. Following intense treatment with high SPS concentration at high temperature the biochar samples were characterized and tested for the degradation of sulfamethoxazole (SMX) in water matrices. The SPS treatment was found to alter significantly the biochar’s surface by dissolving the inorganic deposits and part of the organic phase. SPS was also found to increase the specific surface area and to change the acidity / basicity of the biochar. Lengthy treatments reduce the catalytic activity, an effect attributed to the oxidation of surface carbon groups, while shorter treatments result in higher activity due to the high specific surface area, enrichment of the surface with carbon groups and limited oxidation of the biochar.

The selective liquid phase hydrogenation of furfural to furfuryl alcohol over Pt nanoparticles supported on SiO2, ZnO, γ-Al2O3, CeO2 is reported under extremely mild conditions. Ambient hydrogen pressure, and temperatures as low as 50 °C are shown sufficient to drive furfural hydrogenation with high conversion and >99% selectivity to furfuryl alcohol. Strong support and solvent dependencies are observed, with methanol and n-butanol proving excellent solvents for promoting high furfuryl alcohol yields over uniformly dispersed 4 nm Pt nanoparticles over MgO, CeO2 and γ-Al2O3. In contrast, non-polar solvents conferred poor furfural conversion, while ethanol favored acetal by-product formation. Furfural selective hydrogenation can be tuned through controlling the oxide support, reaction solvent and temperature.

The formation of copper-based catalysts ranging from nanoparticles to isolated and dimeric Cu species supported on nanophased alumina is reported and utilised for the catalytic liquid-phase hydrogenation of furfural. The materials were synthesised via wet impregnation using various copper precursors (nitrate, acetate and sulphate) at two different loadings. A high Cu loading (5.0 wt.%) led to the formation of well-defined nanoparticles, while a lower loading (1.0 wt.%) generated a highly dispersed phase consisting mostly of atomic and dimeric Cu species dispersed on Al2O3. The catalytic reaction was found to be structure sensitive, promoting decarbonylation reactions with low Cu loading. Copper sulphate derived catalysts were found to severely decrease furfuryl alcohol selectivity from 94.6% to 0.8%, promoting the formation of side reactions. The sulphur-free catalysts represent a greener and more sustainable alternative to the toxic catalysts currently used in industry, operating at milder conditions of 50 °C and 1.5 bar H2.

The effect of the morphology of Ir particles supported on γ-Al2O3, 8 mol%Y2O3-stabilized ZrO2 (YSZ), 10 mol%Gd2O3-doped CeO2 (GDC) and 80 wt%Al2O3–10 wt%CeO2–10 wt%ZrO2 (ACZ) on their stability on oxidative conditions, the associated metal–support interactions and activity for catalytic decomposition of N2O has been studied. Supports with intermediate or high oxygen ion lability (GDC and ACZ) effectively stabilized Ir nanoparticles against sintering, in striking contrast to supports offering negligible or low oxygen ion lability (γ-Al2O3 and YSZ). Turnover frequency studies using size-controlled Ir particles showed strong structure sensitivity, de-N2O catalysis being favoured on large catalyst particles. Although metallic Ir showed some de-N2O activity, IrO2 was more active, possibly present as a superficial overlayer on the iridium particles under reaction conditions. Support-induced turnover rate modifications, resulted from an effective double layer [Oδ−–δ+](Ir) on the surface of iridium nanoparticles, via O2− backspillover from the support, were significant in the case of GDC and ACZ., IVY acknowledges Technical University of Crete for partial financial support. MJT acknowledges Aston University for a PhD scholarship. GK acknowledges funding from the Royal Society and EPSRC.

© 2014 American Chemical Society. Scanning tunneling microscopy, temperature-programmed reaction, near-edge X-ray absorption fine structure spectroscopy, and density functional theory calculations were used to study the adsorption and reactions of phenylacetylene and chlorobenzene on Ag(100). In the absence of solvent molecules and additives, these molecules underwent homocoupling and Sonogashira cross-coupling in an unambiguously heterogeneous mode. Of particular interest is the use of silver, previously unexplored, and chlorobenzene-normally regarded as relatively inert in such reactions. Both molecules adopt an essentially flat-lying conformation for which the observed and calculated adsorption energies are in reasonable agreement. Their magnitudes indicate that in both cases adsorption is predominantly due to dispersion forces for which interaction nevertheless leads to chemical activation and reaction. Both adsorbates exhibited pronounced island formation, thought to limit chemical activity under the conditions used and posited to occur at island boundaries, as was indeed observed in the case of phenylacetylene. The implications of these findings for the development of practical catalytic systems are considered.

Nanoparticulate gold has emerged as a promising catalyst for diverse mild and efficient selective aerobic oxidations. However, the mechanism of such atom-economical transformations, and synergy with functional supports, remains poorly understood. Alkali-free Mg-Al hydrotalcites are excellent solid base catalysts for the aerobic oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furan dicarboxylic acid (FDCA), but only in concert with high concentrations of metallic gold nanoparticles. In the absence of soluble base, competitive adsorption between strongly-bound HMF and reactively-formed oxidation intermediates site-blocks gold. Aqueous NaOH dramatically promotes solution phase HMF activation, liberating free gold sites able to activate the alcohol function within the metastable 5-hydroxymethyl-2-furancarboxylic acid (HMFCA) reactive intermediate. Synergistic effects between moderate strength base sites within alkali-free hydrotalcites and high gold surface concentrations can afford highly selective and entirely heterogeneous catalysts for aqueous phase aldehyde and alcohol cascade oxidations pertinent to biomass transformation.

Narrow@band photoconductivity with a spectral width of 0.16 eV is obtained from solution@ processed colloidal ZnO nanocrystals beneath the band@edge at 2.25 eV. A new model involving electron transfer from deep defects to discrete sha llow donors is introduced to explain the narrow spectrum and the exponential form of the current rise and decay transients. The defects are tentatively assigned to neutral oxygen vacancies. The photocurrent responsivity can be enhanced by storage in air and this correlates with the form ation of carbonate surface species by capture of carbon dioxide during storage. This controllability is exploited to develop a low@cost and scalable photolithographic approach to pixelate photodetectors for applications such as object discrimination, sensing etc. The spectral response can be spatially patterned so that dual (ultraviolet and green) and single (ultraviolet only) wavelength detecting ZnO pixels can be produced on the same substrate. This presents a new sensor mode with applications in security or full colour imaging.

Opportunistic communications through wireless ad-hoc mesh networks have been thoroughly studied in the context of military infrastructureless deployments, sensor networks and even human-centered pervasive networking. However, due to the lack of a model that accurately computes the probability distribution of the delay, we usually content ourselves with the mean values. Such an approach can limit both the ability to predict the system's behavior and the ways to affect it. In this paper, we present an analytical framework that allows us to estimate the probability distribution of the delay as a function of the field size, the number of participating users and the movement model. In addition, the short computational time, as compared to simulations, allows us to analyze systems that would otherwise be infeasible, due to their size. The derived delay probability distribution can help us decide whether opportunistic networking can be practically used in, e.g., dense vehicular environments, highly volatile mesh networks, or even predicting a successful marketing campaign. We validate the analytical results against a simulation of the presented model. Furthermore, we created a second, highly sophisticated and realistic, simulation, in order to verify the validity of the observed trends in almost-real-life situations.

Biochar and hydrochar prepared from pyrolysis and microwave-assisted hydrothermal carbonization of Prosopis africana shell respectively were used as adsorbents for the removal Pb2+ and Cd2+ from aqueous solution using batch adsorption technique. The materials proved to have good adsorption capacities and higher than some previously studied adsorbents. Maximum adsorption capacities for the hydrochar and biochar were 45.3 and 31.3 mg/g for Pb2+ and 38.3 and 29.9 mg/g for Cd2+, respectively. The adsorption process followed pseudo-second-order kinetics and the adsorption data fitted the Langmuir isotherm model. These materials could therefore be used as a low cost adsorbents in wastewater treatment.

A new microwave-assisted hydrothermal synthesis of carbon monolith is reported in this work. The process uses microwave heating at 100 °C under acidic condition by employing a triblock copolymer F127 as the template, and resorcinol–formaldehyde as the carbon precursor. Scanning electron microscopy, Fourier transform infrared spectroscopy, nitrogen sorption measurements, transmission electron microscopy, X-ray studies and thermogravimetic analysis were used to characterize the synthesized material. The carbon monolith is crack-free, mesoporous and has a high surface area of 697 m2/g. The results demonstrate that the microwave-assisted hydrothermal synthesis is a fast and simple approach to obtain carbon monoliths, as it reduces effectively the synthesis time from hours to a few minutes which could be an advantage in the large scale production of the material.

Spillover of reactants from one active site to another is important in heterogeneous catalysis and has recently been shown to enhance hydrogen storage in a variety of materials. The spillover of hydrogen is notoriously hard to detect or control. We report herein that the hydrogen spillover pathway on a Pd/Cu alloy can be controlled by reversible adsorption of a spectator molecule. Pd atoms in the Cu surface serve as hydrogen dissociation sites from which H atoms can spillover onto surrounding Cu regions. Selective adsorption of CO at these atomic Pd sites is shown to either prevent the uptake of hydrogen on, or inhibit its desorption from, the surface. In this way, the hydrogen coverage on the whole surface can be controlled by molecular adsorption at a minority site, which we term a 'molecular cork' effect. We show that the molecular cork effect is present during a surface catalysed hydrogenation reaction and illustrate how it can be used as a method for controlling uptake and release of hydrogen in a model storage system.