Search

International audience; Reaching high selectivity at high conversion and high rate in the industrially important selective hydrogenation of α,β-unsaturated aldehydes is a challenging task. Among current approaches reported in the literature, high selectivity towards the unsaturated alcohol or saturated aldehyde is generally achieved at the expense of activity. The use of bimetallic systems can lead either to selectivity or to activity enhancement, but generally not to both. Herein, we show that, for cinnamaldehyde hydrogenation, combining Ni nanoparticles (NiNP) and Ru single atoms (RuSA) on CNTs allows improvement of the hydrocinnamaldehyde selectivity, while obtaining a remarkable activity. The STY of RuSA-NiNP/CNT is approximately 60 times higher than that of the RuSA/CNT and 10 times higher than that of the NiNP/CNT. Importantly, the resulting catalyst shows 94% selectivity at 99% conversion and a good stability in flow. Insights into the cooperative “cocktail”-type catalysis between NiNP and RuSA were revealed from density functional theory calculations.

Funding: This research was funded by the UK Science and Technology Facilities Council via direct access proposal (RB1920033, VESUVIO). Hydrogen spillover is an elusive process, and its characterization, using experimental probes and ab initio modeling, poses a serious challenge. In this work, the nuclear quantum dynamics of hydrogen in a palladium-decorated cubic polymorph of tungsten oxide, Pd/cWO3, are characterized by the technique of neutron Compton scattering augmented by ab initio harmonic lattice modeling. The deeply penetrating nature of the neutron scattering process, the lack of spectroscopic selection rules, the inherent high sensitivity to hydrogen, the high energy and momentum resolution for hydrogen, and the mass selectivity of the technique render the neutron Compton scattering a very potent and unique tool for investigating the local dynamics of hydrogen species in bulk matrices. The total neutron Compton scattering response of hydrogen is described in terms of the hydrogen momentum distribution. The distribution is deconvoluted under the assumption of three pools of hydrogen with distinctly different nuclear quantum dynamical behavior: (i) hydrogen-terminated beta-palladium hydride, (ii) hydrogen in acid centers (OH+ groups) on the surface of the cubic phase of tungsten oxide, and (iii) quasi-free atomic hydrogen inside the saturated hydrogen bronze resulting from the spillover process. The ab initio modeling of lattice dynamics yields theoretical predictions for the values of the widths of proton momentum distributions in the first two hydrogen pools, which allows for obtaining the contribution and the width of the momentum distribution of the quasi-free atomic hydrogen resulting from the hydrogen spillover process. The analysis reveals that the local binding strength of the quasi-free hydrogen is characterized by the values of nuclear momentum distribution width, nuclear kinetic energy, and force constant of the underlying potential of the mean force close to those of free, unconstrained hydrogen atomic species in a gas of non-interacting particles described by the Maxwell–Boltzmann distribution. Moreover, this picture of the local dynamics of the quasi-free hydrogen is consistent with the proton polaron model of hydrogen-induced coloration of bulk hydrogenated WO3. Publisher PDF

Metal confinement catalyst MoS2/Pt@TD-6%Ti (TD, TS-1/Dendritic mesoporous silica nanoparticles composite) in dendritic hierarchical pore structures was synthesized and showed excellent sulfur-resistance performance and stabilities in catalytic hydrodesulfurization reactions of probe sulfide molecules. The MoS2/Pt@TD-6%Ti catalyst combines the concepts of Pt-confinement effect and hydrogen spillover of Pt noble metal. The modified micropores of Mo/Pt@TD-6%Ti only allow the migration and dissociation of small H2 molecules (0.289 nm), and effectively keep the sulfur-containing compounds (e.g. H2S, 0.362 nm) outside. Thus, the MoS2/Pt@TD-6%Ti catalyst exhibits higher DBT and 4,6-DMDBT HDS activities because of the synergistic effect of the strong H2 dissociation ability of Pt and desulfurization ability of MoS2 with a lower catalyst cost. This new concept combining H2 dissociation performance of noble metal catalyst with the desulfurization ability of transition metal sulfide MoS2 can protect the noble metal catalyst avoiding deactivation and poison, and finally guarantee the higher activities for DBT and 4,6-DMDBT HDS.

The morphologies and the electron property of catalysts play the very important roles in the hydrogenation and dehydrogenation of liquid organic hydrogen carriers (LOHCs) such as dibenzyltoluene (DBT). The different morphologies and pore structures of γ-Al2O3 and MoxC doped γ-Al2O3 were synthesized as the supports for Pt catalysts. After analyzing of various characterizations and catalytic testing, it was found that the large surface area and the mesoporous structure of catalysts are beneficial to both DBT hydrogenation and perhydro-dibenzyltoluene (H18-DBT) dehydrogenation. The doping of MoxC promoted the formation of the smaller Pt nanoparticles and increased Pt dispersion. The forming Pt–Mo structure is beneficial to hydrogen spillover which suppress the formation of by-product. The high Pt dispersion of 0.1 wt% MoxC doped Pt/Al2O3 catalyst plays the positive roles in increasing H18-DBT dehydrogenation activity.

On-site produced hydrogen from ammonia decomposition can directly fuel solid oxide fuel cells (SOFCs) for power generation. The key issue in ammonia decomposition is to improve the activity and stability of the reaction at low temperatures. In this study, proton-conducting oxides, Ba(Zr,Y) O3-δ (BZY), were investigated as potential support materials to load Ni metal by a one-step impregnation method. The influence of Ni loading, Ba loading, and synthesis temperature, of Ni/BZY catalysts on the catalytic activity for ammonia decomposition were investigated. The Ni/BZY catalyst with Ba loading of 20 wt%, Ni loading of 30 wt%, and synthesized at 900 °C attained the highest ammonia conversion of 100% at 600 °C. The kinetics analysis revealed that for Ni/BZY catalyst, the hydrogen poisoning effect for ammonia decomposition was significantly suppressed. The reaction order of hydrogen for the optimized Ni/BZY catalyst was estimated as low as −0.07, which is the lowest to the best of our knowledge, resulting in the improvement in the activity. H2 temperature programmed reduction and desorption analysis results suggested that a strong interaction between Ni and BZY support as well as the hydrogen storage capability of the proton-conducting support might be responsible for the promotion of ammonia decomposition on Ni/BZY. Based on the experimental data, a mechanism of hydrogen spillover from Ni to BZY support is proposed.

Identifying optimal Ru size in NH3 synthesis can improve reaction activity and maximize the utilization of Ru to reduce catalyst cost. However, previous researches are focused on large Ru particle size (≥ 2 nm) while that below 2 nm in NH3 synthesis is unclear. Here we synthesized a series of Rux/BaCeO3 with different Ru sizes (x=1.1–3.0 nm) through size-controlled Ru colloid. With the decrease of Ru size, NH3 synthesis rate over Ru1.1/BaCeO3 increases to 19.4 mmol gcat−1 h−1 at 400°C and 1 MPa, which is 5.7 times that of Ru3.0/BaCeO3 and superior to most of Ru-based catalysts previously reported. It reveals that the reduction of Ru size enhances the generation of Ce3+ and oxygen vacancies in BaCeO3, which can donate electron to Ru centers and promote N2 dissociation. Moreover, the small Ru size enhances hydrogen spillover from Ru to BaCeO3 to alleviate hydrogen poisoning, resulting in efficient NH3 synthesis.

The requirements for the efficient replacement of fossil fuel, combined with the growing energy crisis, places focus on hydrogen production. Efficient and cost-effective electrocatalysts are needed for H2 production, and novel strategies for their discovery must be developed. Here, we utilized Kinetic Monte Carlo (KMC) simulations to demonstrate that hydrogen evolution reaction (HER) can be boosted via hydrogen spillover to the support when the catalyst surface is largely covered by adsorbed hydrogen under operating conditions. Based on the insights from KMC, we synthesized a series of reduced graphene-oxide-supported catalysts and compared their activities towards HER in alkaline media with that of corresponding pure metals. For Ag, Au, and Zn, the support effect is negative, but for Pt, Pd, Fe, Co, and Ni, the presence of the support enhances HER activity. The HER volcano, constructed using calculated hydrogen binding energies and measured HER activities, shows a positive shift of the strong binding branch. This work demonstrates the possibilities of metal–support interface engineering for producing effective HER catalysts and provides general guidelines for choosing novel catalyst–support combinations for electrocatalytic hydrogen production.

Sulfur poisoning of noble metal catalysts has been a major challenge for decades. This work demonstrates the superior sulfur tolerance of a hybrid zeolite-supported Pd catalyst for hydrogenation of tetralin containing benzothiophene. The hybrid catalyst consists of Pd supported on a large-pore acidic zeolite Y (Pd/HY) and a small-pore zeolite A without (Pd/HA) or with surface metal passivation by chemical vapor deposition of SiO2 (SiO2-Pd/HA) and with potassium ion exchange (SiO2-Pd/KA). Pd/HY is very active for tetralin hydrogenation but quickly deactivates after exposure to benzothiophene at high concentration of 100 ppm sulfur. The SiO2-coated Pd/HA shows no activity for tetralin hydrogenation, but continues to activate H2 and serve as a source of hydrogen spillover from Pd/HA since these metal sites are protected from thiophenic sulfur due to size-selective exclusion. Adding K ion-exchanged and SiO2-coated catalyst SiO2 -Pd/KA to Pd/HY is even more effective for enhancing sulfur tolerance, both for tetralin hydrogenation and for isomerization of cis-decalin to trans-decalin in the presence of benzothiophene. The turnover frequencies (TOF) of all the catalysts are similar at the exposed sulfur/Pd atomic ratio of around 0.5. With further increase in sulfur/Pd ratio, rapid decline in TOF was observed on Pd/HY, but SiO2-Pd/KA + Pd/HY hybrid catalyst shows a significantly higher TOF than that over Pd/HY, even though SiO2-Pd/KA or SiO2-Pd/HA alone shows no TOF for tetralin hydrogenation. Even after high-dose poisoning at 400 ppm sulfur, the SiO2-Pd/KA + Pd/HY hybrid recovered activity more quickly than SiO2-Pd/HA + Pd/HY, while the latter in turn is much better than Pd/HY alone. These results point to the higher activity for hydrogen spillover from SiO2-Pd/KA where Pd metal sites are protected from not only thiophenic sulfur but also inorganic sulfur H2S by shape-selective exclusion. The present work further establishes the validity of shape-selective exclusion and hydrogen spillover in the design concept proposed for a sulfur-tolerant bimodal acidic zeolite-supported metal catalyst for hydrogenation of naphthalene [C.S. Song, Chemtech, 29 (1999) 26–30], and refines the design concept further for limiting the size of small pore in hybrid catalysts to ∼ 3 A for restricting access of H2S but allowing entrance of H2. This refined design concept is applicable to other supported monometallic and bimetallic catalysts.

The development of an efficient hydrogen spillover (HS) catalyst achieves the stoichiometric chemoselective hydrogenation of NO3− and NO2− into N2 at room temperature, which is extremely challenging. Herein, we report a CuxPd1−x nanowire network (NWN) (x = 7, 5, or 3) with tunable hydrogen spillover rate of formic acid (FA) with polyvinylpyrrolidine imine (PVPI) modifying its surface. The presence of PVPI boosts the catalytic selectivity and activity of CuPd NWN for FA dehydrogenation and, more importantly, serves as a modem to tune the HS rate of FA and to stoichiometrically hydrogenate NO3− and NO2− to N2 at room temperature. The density functional theory (DFT) reveals that the CuPd (130 h−1) has a weaker HS rate than AgPd (390 h−1), but the CuPd (> 99%) has a higher utilization of HS than AgPd (31%). Our studies demonstrate a new approach of tuning the FA HS rate and maximizing the application for stoichiometric chemoselective hydrogenation reaction, which will be important for hydrogen generation and its applications.

Defect engineering of metal oxides is a facile and promising strategy to improve their photocatalytic activity. In the present study, Pt/TiO2-x was prepared by a reduction treatment assisted by hydrogen spillover to pure rutile, anatase, and brookite and was subsequently used for hydrogen production from an aqueous methanol solution. With increasing reduction temperature, the photocatalytic activity of the rutile Pt/TiO2-x increased substantially, whereas the activity of anatase Pt/TiO2-x decreased and that of brookite Pt/TiO2-x was independent of the treatment temperature. Electron-spin resonance analysis revealed that rutile and brookite possess similar defect sites (Ti3+ and concomitant oxygen vacancy) after the reduction at 600 °C, whereas different resonance signals were observed for anatase after the reduction at 600 °C. During the reduction process, electrons donated from spillover hydrogen migrate between the conduction band and the inherent midgap states. This research demonstrates that the depth of the inherent midgap states, depending on the crystal phases, influences the generation of defects, which play a key role in the photocatalytic performance of Pt/TiO2-x.

Here we exquisitely fabricated Cu/ZrO2-dp catalysts with plentiful Cu-ZrO2 interfaces by depositing amorphous ZrO2 onto Cu nanoparticles for the hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL). With the created plentiful Cu-ZrO2 interfaces, the optimal catalyst 3Cu/ZrO2-dp exhibited exceptional catalytic performance under mild reaction conditions, and achieved the highest GVL mass productivity of 266.0 mmol GVL·h−1·g−1 Cu, which was 12.5 and 2.3 times of Cu/ZrO2 catalysts with equivalent Cu loadings prepared by traditional impregnation (3Cu/ZrO2-im) or co-precipitation (3Cu/ZrO2-cp). As far as we know, this GVL mass productivity stood at the highest level compared with those obtained using non-noble metal catalysts under similar reaction conditions. By systematic investigation with multiple characterizations, density functional theory (DFT) calculations, and kinetic studies, it was found that interfacial active centers were created at Cu-ZrO2 interfaces, which contained oxygen vacancies (Ov), negatively charged Cuδ− and partially reduced Zr3+. The Ov favored the adsorption and activation of LA via its ketone group, while negatively charged Cuδ− was able to enhance heterolysis of H2, which resulted in the formation of H+-Cuδ− and Zr3+-H− active species via hydrogen spillover. Also, plentiful acid sites, which derived from coordinatively unsaturated and defective Zr species, generated at Cu-ZrO2 interfaces. With the cooperation of interfacial active centers (Cuδ−-Ov-Zr3+) and acid sites, the fabricated 3Cu/ZrO2-dp with plentiful Cu-ZrO2 interfaces achieved excellent catalytic performance for the hydrogenation of LA to GVL. Hence, the synergistic catalysis of Cu-ZrO2 interfaces provided an effective strategy for designing catalysts with a satisfactory performance for the hydrogenation of LA, which also can be expanded to other hydrodeoxygenation reactions.

Side reactions competing with propane dehydrogenation were studied on K-PtSn/Al2O3 and SnOx/SiO2 catalysts. The results showed that hydrogenolysis, hydrogenation, deep dehydrogenation, and coke formation occurred more pronouncedly on K-PtSn/Al2O3, contrasting with the catalytic cracking result. Because of the higher total acidity on SnOx/SiO2, measured by NH3-TPD, more catalytic cracking occurred on this catalyst. However, SnOx/SiO2 showed a lower coke deposition, although the acid site can promote the coke formation. This contrast was not due to the spillover effect, which can suppress coke formation on the acid site. Essentially, the propylene hydrogenation, H2-TPD, and FTIR results demonstrate that SnOx/SiO2 had a lower hydrogen spillover than that of K-PtSn/Al2O3. On the other hand, TPO results from propylene dehydrogenation and coke formation of propadiene illustrate that the key of distinguished SnOx/SiO2 catalyst stability was owing to a low ability of coke precursor generation.

Efficient transition metal oxide electrocatalysts for the alkaline hydrogen evolution reaction (HER) have received intensive attention to energy conversion but are limited by their sluggish water dissociation and unfavorable hydrogen migration and coupling. Herein, systematic density functional theory (DFT) predicts that on representative NiO, the hydroxylation (OH-) and heterointerface coupled with metallic Cu can respectively reduce the energy barrier of water dissociation and facilitate hydrogen spillover. Motivated by theoretical predictions, we subtly designed a delicate strategy to realize the electrochemical OH- modification in KOH with moderate concentration (HOM-NiO) and to channel rapid hydrogen spillover at the heterointerface of HOM-NiO and Cu, ensuring an enhanced HER kinetic. This HOM-NiO/Cu is systematically investigated by in situ XAS and electrochemical simulations, verifying its extraordinary merits for HER including the enhanced water dissociation, alleviated oxophilicity that is advantageous for consecutive adsorptions of water, and accelerated hydrogen spillover, thereby exhibiting superb HER activity with 33 and 310 mV overpotentials at the current densities of 10 and 1000 mA cm-2 in 1.0 M KOH, outperforming the Pt/C. This study might provide a reasonable strategy for the functionalized design of superior electrocatalysts.

A new variety of CdS/NiO core-shell p-n heterojunction is synthesized by in-situ chemically depositing NiO shell on single-crystal CdS nanorods for the first time. With this method, the range of NiO shell thickness can be accurately controlled within a few nanometers. The optimized CdS/NiO sample (CSN0.5) with a NiO shell layer of 1.5 nm exhibits a highly efficient photocatalytic H2 evolution rate of 731.7 μmol/h (corresponding to 243.9 mmol/g/h) without using co-catalyst, which is among the highest value of all the CdS-based photocatalysts. The apparent quantum efficiency (AQE) of CSN0.5 at 365 nm wavelength reaches 28.19%. The remarkably enhanced photocatalytic performance can be attributed to a hydrogen spillover effect induced by ascorbic acid in CdS/NiO, which promotes the transmission of adsorbed H* from hydrogen-rich NiO (electron-poor region) to hydrogen-poor CdS (electron-rich region) where the adsorbed H* reacts in time with the photogenerated electron to produce H2, facilitating the H2 evolution reaction. This work provides a method to promote the photocatalytic H2 evolution reaction by using hydrogen spillover effect.

Plastics waste has become a major environmental threat, with polyethylene being one of the most produced and hardest to recycle plastics. Hydrogenolysis is potentially the most viable catalytic technology for recycling. Ruthenium (Ru) is one of the most active hydrogenolysis catalysts but yields too much methane. Here we introduce ruthenium supported on tungstated zirconia (Ru-WZr) for hydrogenolysis of low-density polyethylene (LDPE). We show that the Ru-WZr catalysts suppress methane formation and produce a product distribution in the diesel and wax/lubricant base-oil range unattainable by Ru-Zr and other Ru-supported catalysts. Importantly, the enhanced performance is showcased for real-world, single-use LDPE consumables. Reactivity studies combined with characterization and density functional theory calculations reveal that highly dispersed (WO x )n clusters store H as surface hydroxyls by spillover. We correlate this hydrogen storage mechanism with hydrogenation and desorption of long alkyl intermediates that would otherwise undergo further C-C scission to produce methane.

As a hydrogen storage material, palladium nanoparticle decorated nitrogen doped graphene (Pd/N-rGO) has drawn much attention owing to its high absorption capacity at moderate conditions. However, its hydrogen absorption-desorption cycle performance, which is essential for their practical application, has been rarely studied. In this paper, a simple and convenient high temperature thermal reduction method was used to synthesize nitrogen-doped graphene decorated with Pd nanoparticles (Pd/N-rGO). Taken it as a representative, the hydrogen absorption-desorption cycle performance of Pd/N-rGO was investigated. The results showed that after three cycles the hydrogen storage capacity dropped from 2.9 ​wt% to 0.8 ​wt% at 25 ​°C and 4 ​MPa pressure. It was found that the palladium nanoparticles shed from Pd/N-RGO sheet after cycle performance test, and then agglomerated. These phenomena will weaken the hydrogen spillover effect, leading to the decrease of hydrogen storage capacity. Meanwhile, decreased defects reduce the hydrogen absorption sites, which will thus deteriorate the hydrogen storage capacity.

Currently, the highly efficient conversion of biomass resources into highly valuable chemicals and biofuels is one of the most prospective approaches to reduce greenhouse gases emission and environmental pollution caused by excess consumption of fossil fuels. Herein, three-dimensional pompon-like well-defined RuCo particles with tunable crystallographic structures and surface atomically dispersed Ru atoms were constructed and intensively investigated as support-free metal catalysts in the hydrodeoxygenation (HDO) of lignin-derived guaiacol. It was demonstrated that the 300 °C-reduced RuCo sample possessed the hexagonal close-packed (hcp ) crystallographic structure with surface abundant atomically dispersed Ru atoms, whereas 600 °C-reduced RuCo sample presented the face-centered cubic phase with lower surface Ru concentration. The as-fabricated RuCo-300 sample showed excellent catalytic HDO activity with a high cyclohexane yield of 85.3%. Comprehensive structural characterizations unveiled that the introduction of atomically dispersed Ru atoms into the RuCo-300 favored the formation of abundant surface Ru-Co sites, as well as electron-rich Ru 0, and such-constructed Ru-Co sites were highly beneficial to the hydrogen dissociation on single Ru0 atoms and the further hydrogen spillover to adjacent Co0 atoms to promote the HDO process. Moreover, density functional theory (DFT) calculations revealed that the hcp structure of RuCo catalysts benefited the adsorption of guaiacol. The unique pompon-like microstructure of RuCo catalysts was conducive to the exposure of active sites and provided more open channels for the easy diffusion of reactants and products. Over the RuCo-300 catalyst, the guaiacol HDO could proceed rapidly via an initial demethoxylation reaction. The present Ru-Co synergetic catalysis in the structure of RuCo catalysts would provide a new strategy for constructing robust heterogeneous bimetal catalysts applied in practical HDO processes of a variety of lignin-derived phenolic compounds.

High-entropy alloys (HEAs) have been intensively pursued as potentially advanced materials because of their exceptional properties. However, the facile fabrication of nanometer-sized HEAs over conventional catalyst supports remains challenging, and the design of rational synthetic protocols would permit the development of innovative catalysts with a wide range of potential compositions. Herein, we demonstrate that titanium dioxide (TiO2) is a promising platform for the low-temperature synthesis of supported CoNiCuRuPd HEA nanoparticles (NPs) at 400 °C. This process is driven by the pronounced hydrogen spillover effect on TiO2 in conjunction with coupled proton/electron transfer. The CoNiCuRuPd HEA NPs on TiO2 produced in this work were found to be both active and extremely durable during the CO2 hydrogenation reaction. Characterization by means of various in situ techniques and theoretical calculations elucidated that cocktail effect and sluggish diffusion originating from the synergistic effect obtained by this combination of elements., Facile fabrication of high-entropy alloys (HEAs) nanoparticles (NPs) on conventional catalyst supports remains challenging. Here the authors show TiO2 is a promising platform for the low-temperature synthesis of supported CoNiCuRuPd HEA NPs with excellent activity and durability in CO2 hydrogenation.

The spillover of hydrogen on an inorganic oxide support is studied using DFT calculations. Quantum-chemical calculations for model catalytic sites with structure H(–Al–O–)3(OH)6 and HH+(‒Al–O–)3(OH)6 are performed using the DFT B3LYP/6-31G * energy functional versus electron density with full energy optimization and calculation of the frequencies of normal vibrations. Geometric parameters, electronic characteristics, distribution of electron density, total energies, energies and entropies of transformation, and frequencies of normal vibrations are calculated for the compounds. The geometric structure of molecules and frequencies of normal vibrations are determined using 6-31G* atomic basis sets. The activation energy of hydrogen transfer is determined for these complexes. It is found that an additional positive charge on a catalytic center HH+(–Al–O–)3(OH)6 sharply lowers the activation energy of hydrogen transfer, the value of which is 13.92 kcal/mol. It is shown that the formation of a complex of water with catalytic center HH+(–Al–O–)3(OH)6 further reduces the activation energy of hydrogen transfer to 5.45 kcal/mol, in agreement with the experimental values of the activation energy of spillover hydrogen on aluminum oxide. The mechanism of the hydrogen transfer reaction in a complex of adsorbed water with a charged catalytic center HH+(‒Al–O–)3(OH)6 adequately reflects the mechanism of hydrogen spillover over an inorganic oxide carrier.

In this study, the hydrogen storage capacity of purified multiwalled carbon nanotubes (MWCNTs) was enhanced from 13- to 15-fold at a temperature of 298 K and pressure of 2.0 MPa, upon incorporation of 1.57–1.88 wt% of ultrafine Ti nanoparticles. The effect of a hydrogen spillover Ti catalyst on MWCNTs prepared using the sputtering method was investigated. A comparison between the hydrogen uptake by MWCNTs sputtered with Ti for 3000 s and that for 6000 s was also performed using the Sievert's volumetric apparatus. The significant enhancement in hydrogen uptake was attributed to the interfacial diffusion of hydrogen from Ti to the MWCNTs. The re-adsorption of hydrogen on the pristine MWCNTs and Ti-decorated MWCNTs dehydrogenated at 200 °C indicated that the samples did not compromise their reversible hydrogen uptake during the hydrogenation–dehydrogenation cycles. It was also found that longer exposure of Ti to the MWCNTs during sputtering improved the hydrogen storage capacity. This improvement could be attributed to the presence of a higher amount of Ti deposited on the MWCNTs, as indicated by thermogravimetric analysis study.

The process of hydrogen spillover on metal nanoparticle decorated carbon surfaces has been discussed for many years due to its importance for heterogeneous catalysis and hydrogen storage. The prese...

The one-pot direct conversion of levulinic acid (LA) to 1,4-pentanediol (1,4-PDO) was investigated over a trimetallic Zn-promoted Cu–Ni alloy on a H-ZSM-5 (Cu–Ni–Zn/H-ZSM-5) catalyst. Under mild re...

The reaction between spillover hydrogen (SH) and mexidol upon high-temperature solid state catalytic isotope exchange (HSCIE) is studied experimentally and via DFT B3LYP and MP2 calculations. The distribution of isotopes and the activation energy of the reaction are determined via NMR spectro-scopy and mass spectrometry for samples of the deuterium-labeled mexidol obtained via HSCIE at 50–120°C. The DFT calculated activation energy of hydrogen transfer on the charged alumina cluster HH+(‒Al–O–)3(OH)6 is found to agree with the experimental data. A mechanism is proposed for HSCIE between the adsorbed compound and charged Bronsted acid sites formed on the surface of the support upon exposure to hydrogen spillover.

The Platinum (Pt)-based catalysts exhibit excellent catalytic performance for the hydrogen evolution reaction (HER) while suffering from poor stability due to the weak interaction between the carbon support and Pt. Herein, a molybdenum-doped titanium dioxide (Ti0.9Mo0.1O2) supported low-Pt electrocatalyst with stronger interaction between catalyst and support is applied to tune the electrocatalytic performance of Pt. The Ti0.9Mo0.1O2 support can not only tolerate the corrosion environment in the catalytic system, but also generate strong metal-support interaction (SMSI) between the oxide and catalyst. A facile solvothermal method is used to prepare Ti0.9Mo0.1O2 as support to anchor Pt nanoparticles. The 5% Pt supported on Ti0.9Mo0.1O2 catalyst exhibits 4.4-fold mass activity (MA) at an overpotential of 50 mV and higher stability than 20% Pt/C with only 1/4 Pt loading. The SMSI between the Ti0.9Mo0.1O2 and Pt prevents the Pt aggregation to achieve excellent stability, and hydrogen spillover effect in the interface between Pt and support benefits the hydrogen production process. This work presents a novel sight for the fabrication and design of oxide supported catalysts in various catalytic system by reasonably employing support effect.

In this work, a new kind of CdS–ZnO core–shell nanorods with controlled ZnO shell are first synthesized by a simple chemical deposition method in aqueous solution. The thickness and distribution of the ZnO shell can be accurately adjusted, and intimate contact interfaces between CdS and ZnO are well constructed. The optimal CSZ0.5 core–shell heterostructure exhibits a photocatalytic H2 evolution rate of 805.5 μmol h−1 without co-catalysts (3 mg of catalyst, equal to 268.5 mmol g−1 h−1), which is 12 and 895 times higher than that of CdS and ZnO, respectively, and is the maximum value among CdS-based photocatalysts under similar experimental conditions. The significant enhancement in the photocatalytic H2 evolution rate can be mainly attributed to three positive factors: the single-crystalline structure of CdS, the Z-scheme mechanism formed between CdS and ZnO, and the introduced ascorbic acid. The first two factors effectively promote the separation and migration of charge carriers, and the latter factor realizes efficient hydrogen spillover for CdS/ZnO to accelerate the photocatalytic hydrogen evolution reaction. In addition, the homogeneous ZnO shell grown on the CdS core efficiently suppresses the photo-corrosion of CdS, which endows CdS/ZnO with outstanding photostability.

The extent of hydrogen spillover on two different Pd-based catalysts supported on mesoporous SBA-15 and MCM-41 is quantitatively predicted using a crystallite-scale model, which considers the effect of size and location of crystallites, metal-support interfacial contact, and diffusivity of the adsorbed species on the support surface. The developed model, in combination with a fixed-bed reactor model predicts that in the absence of any reductant in the feed, the NO conversion is higher ( = 37 %) on the SBA-15 supported catalyst as compared to 25 % on MCM-41, which is consistent with the reported data in the literature. The difference in the catalytic activity is ascribed to the different spillover rates of hydrogen on SBA-15 and MCM-41, which is further correlated to the fraction of Pd crystallites present in the support channels. The model is also used to study the effect of cycle time, H2 concentration, Pd dispersion, and Pd loading on NO reduction under cyclic conditions. Consistent with the literature findings, the model predicts that the Pd surface area and the metal-support interfacial contact increase with an increase in the Pd loading and dispersion, which result in higher spillover and hence increase the NO conversion. Even though the present model has been developed for the H2-SCR system, it can also be extended to other catalytic systems where spillover effects are significant.

It is highly desirable to develop a low-pressure, low-temperature ammonia synthesis process. Although this process is, in principle, thermodynamically feasible under ambient conditions, it remains a big challenge to find ideal catalysts with favorable kinetic pathways. Here, we demonstrate that efficient ammonia synthesis (>3700 μg h−1 gcat.−1) from N2 and H2 gases can proceed at room temperature using Mo, Pt modified TiO2−x under visible light irradiation up to 800 nm. The doped Mo(V) species nearby surface oxygen vacancies (VO) offer coordinatively unsaturated sites for N2 activation with strong adsorption energy and excellent electron back-donation ability. Distinctively, a small amount of surface-loaded Pt nanoparticles trigger hydrogen spillover from Pt to VO, enabling facile NH3 assembly and desorption, as well as increasing free Mo(V) active sites. The incorporation of Mo and Pt also synergistically optimizes the light-harvesting ability and the band structure of TiO2, greatly facilitating the photoexcited N2 reduction and H2 oxidation.

International audience; We recently reported (R. Castro Contreras, B. Guicheret, B. F. Machado, C. Rivera-Cárcamo, M. A. Curiel Alvarez, B. Valdez Salas, M. Ruttert, T. Placke, A. Favre Réguillon, L. Vanoye, C. de Bellefon, R. Philippe and P. Serp, J. Catal., 2019, 372, 226–244) that a structure/activity correlation exists in Pd/C catalysts for myrcene hydrogenation, which integrates the Pd dispersion, and the surface concentration of oxygen groups and defects of the support. Here, through a combined experimental–theoretical study, we provide an explanation of the influence of these three structural characteristics of Pd/C catalysts for alkene hydrogenation. Highly dispersed Pd nanoparticles (PdNP) are necessary to activate dihydrogen. A high concentration of surface defects on the support is necessary to stabilize Pd single atoms (PdSA), which coexist with PdNP on Pd/C catalysts. A high concentration of oxygenated surface groups is also necessary on the support to allow hydrogen spillover. We demonstrate that such a combination allows cooperative catalysis to operate between PdNP and PdSA that involves the formation of PdSA–H species, which are much more active than PdNP–H for alkene hydrogenation but also isomerization. Importantly, we also report an efficient method to control the ratio between PdSA and PdNP in Pd/C catalysts of similar loadings and show that the control of this ratio allows the development of a new generation of stable and highly active catalysts integrating the ultra-rational use of precious metals in short supply. Indeed, for myrcene hydrogenation, activity variations of several orders of magnitude were measured as a function of the value of this ratio.

Isolating metal atoms on supports for catalysis has attracted great attention of researchers due to the unique catalytic properties. Here we show by utilizing the hydrogen spillover effect at high temperature (700 °C) that the in situ formed surface oxygen vacancies on TiO2 nanobelts can facilitate the redispersion of Pt nanoparticles to stable single-atoms. The isolated Pt atoms are firmly confined by the surface oxygen vacancy sites in the internal surface of TiO2. Density functional theory (DFT) calculations have further proved that Pt atom is likely to be confined to oxygen vacancies to form single-atom sites. The as-obtained catalyst exhibits excellent photocatalytic water splitting performance with a hydrogen evolution rate of 38.33 mmol mgPt−1 h−1 under simulated solar light irradiation, which is about 59.9 times higher than that of TiO2 nanobelts with Pt nanoparticles. This approach provides a facile method to prepare noble metal catalysts with both high atom economy and reaction activity.

Metallic oxide based catalysts have received much attention in CO2 hydrogenation to methanol because of their high methanol selectivity and long-term stability. But the relatively weak hydrogenation ability leads to low methanol activity. Here, we introduce a small amount of Cu (molar fraction

The selective semihydrogenation of alkynes is of importance in many industrial applications, but great challenges still remain in the full utilization of noble metals for the catalysis of hydrogen spillover on mixed supports. As Pd0 is chemically loaded on Cu2O/TiO2, this work reports that Pd0 is imparted with a high electron density to dissociate H2 efficiently and the active Cu2O hydride is responsible for the high catalytic activity in spillover semihydrogenations. As compared with inert Pd–Cu2O/SiO2 interfaces, the studies demonstrate that the high chemoselectivity and stereoselectivity originate from the well-defined p–n junctions of Cu2O/TiO2, therein alkynes are adsorbed in their trans configurations and the product is desorbed from them. As catalyzed by 1.3Pd–3.6Cu2O/TiO2 in 1 atm H2 at 30 °C, the semihydrogenations can be completed in 90 min with 97.6% chemoselectivity for phenylacetylene, and in 45 min with 92.4% stereoselectivity for methyl non-2-ynoate. These studies provide new ideas to design and synthesize noble metal-based catalysts through manipulating the interface properties of the mixed supports.

The tungsten oxide nanorods loaded with ruthenium nanoparticles (Ru-WO3) nanocomposite were synthesized by hydrothermal method and impregnation method. The properties of Ru-WO3 catalysts were characterized by various methods, such as BET, XRD, SEM, TEM, EDS and XPS. The results show that hydrogen spillover occurs on the surface of WO3 and the catalytic activity of Ru-WO3 in hydrogenation of cyclohexene increases with the increase of reaction time. Subsequently, the Ru-WO3 catalysts was used to hydrogenate N-propylcarbazole (NPCZ). Compare with commercial 0.5 wt% Ru–Al2O3 catalyst, Ru-WO3 can realize the rapid hydrogen uptake of NPCZ at a lower metal loading (0.34 wt%) and lower temperature (150 °C), which is attributed to the increase of reactive sites caused by hydrogen spillover.

Hydrogen sensing simultaneously endowed with fast response, high sensitivity and selectivity is highly desired in detecting hydrogen leakages such as in hydrogen-driven vehicles and space rockets. Here, hydrogen sensing reined via a hydrogen spillover effect has been developed using palladium nanoparticles photochemically decorated on WO3 nanoparticles (Pd-NPs@WO3-NPs). Theoretically, the Pd-NP catalysts and WO3-NP support are used to construct the hydrogen spillover system, in which Pd NPs possess high catalytic activity, promoting the electron transfer and therefore the reaction kinetics. Beneficially, the Pd-NPs@WO3-NP sensor prototypes toward 500 ppm hydrogen simultaneously exhibit fast response time (∼1.2 s), high response (Ra/Rg = 22 867) and selectivity at a working temperature of 50 °C. Such advanced hydrogen sensing provides an experimental basis for the smart detection of hydrogen leakage in the future hydrogen economy.

A rational porous structure can efficiently enhance the electrode reaction process. In this study, we fabricated a type of three-dimensional (3D)-ordered hierarchically porous carbon via a dual-template method to support ruthenium species as efficient cathodes towards the hydrogen evolution reaction (HER). The ordered hierarchical pores comprised of three levels of porous structure, including the inverse opal-structured macroporous carbon skeleton (ca. 150 nm), the internal-ordered mesoporous structure (ca. 5 nm), and abundant microporous structure (

Local coordination environments of isolated metal atoms in single-atom catalysts (SACs) play decisive roles for their catalytic performance. By varying the morphology and P and N heteroatom doping of the CeO2 support, here we showed that the activity of Pt single atoms on spherical CeO2 is about 7 times higher than that on CeO2 nanorods in hydrogenation of phenylacetylene. Doping the spherical CeO2 support using N is more effective than using P, and could enhance the activity by another 3.3 times, which was 2.6-times even higher than that of spherical CeO2 supported Pt clusters. Diffuse reflectance infrared Fourier transform spectroscopy of chemisorbed CO and X-ray photoelectron spectroscopy showed that N doping induced an increase of the electron density of Pt single atoms, opposite to the effect of P doping. H–D exchange and temperature-programmed reduction of hydrogen revealed that a large enhancement of hydrogen dissociation activity and hydrogen spillover by N doping are both essential for promoting the activity for catalytic hydrogenation.

Hydrogen spillover is mechanistically poorly understood, due to the H˙ donor complexity. We show that HV(CO)4dppe (1) transfers H˙ to MoO3 in separate H+ and e− transfer steps. This is analogous to hydrogen spillover from Pt to MoO3 and suggests that 1 is a good model for H˙ adsorbed on Pt.

The effect of hydrogen introduction on Lewis acid transformation to Bronsted acid was investigated over the WOx catalysts supported on different supports (HY-15, HY-500, MCM-22, SiO2, and Al2O3). The Lewis acid transformation on the catalysts was investigated by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of adsorbed NH3 at 100 °C under atmospheric pressure for 130 min. According to the results of in situ DRIFTS, ammonia migration from Lewis acid sites to Bronsted acid sites occurred over the WOx catalysts supported on all different supports. It is proposed that the partial reduction of WOx occurred under the hydrogen atmosphere, resulting in the generation of oxygen vacancies sites. The generated oxygen vacancies of the supported WOx catalysts were found to play an important role for activating the hydrogen spillover, leading to Lewis acid transformation to Bronsted acid. It was suggested that the selected support is the crucial factor for Lewis acid transformation performances. The results from our experiments showed that the weak interaction between WOx and support led to the easy reduction of W species, which promoted the generation of oxygen vacancies sites. The large amount of oxygen vacancies leads to high Lewis acid transformation. Moreover, the influence of different supports was discussed and investigated by several analytical techniques such as H2-TPD, H2-TPR, O2-TPD, UV–vis, XRD, XPS, and TEM-EDS techniques.

Photoelectrochemical N2 reduction reaction (PEC NRR) is a promising method to solve the problems of environmental protection and energy sustainability. However, the strong chemical stability of the N≡N bond and competitive hydrogen evolution reaction (HER) cause the nonideal efficiency of N2 → NH3 conversion in actual operation. For the first time, a Mo2C/C heterostructure was fabricated as a PEC cathode for N2 reduction under environmental conditions. The Mo2C/C heterostructure could effectively decrease the coverage of hydrogen spillover and inhibit the competitive HER, resulting in a desirable selectivity for N2 activation. Meanwhile, the decoration of the C shell further promoted the stability and conductivity of Mo2C. Mo sites of Mo2C were considered as activation centers, which played a dominant role in the final PEC performance. An optimal NH3 yield rate of up to 6.6 μg h-1 mg-1 was achieved with the Mo2C/C heterostructure, which was almost 3 times that with pristine C. The faradic efficiency (FE) of the Mo2C/C heterostructure was 37.2% at 0.2 V (vs Ag/AgCl). This work not only provides an insight into the interplay between the Mo2C/C heterostructure and N2 activation, but also reveals its great potential in NH3 synthesis by a green route.

An In2O3 supported nickel catalyst has been prepared by wet chemical reduction with sodium borohydride (NaBH4) as a reducing agent for selective hydrogenation of carbon dioxide to methanol. Highly dispersed Ni species with intense Ni-In2O3 interaction and enhanced oxygen vacancies have been achieved. The highly dispersed Ni species serve as the active sites for hydrogen activation and hydrogen spillover. Abundant H adatoms are thereby generated for the oxygen vacancy creation on the In2O3 surface. The enhanced surface oxygen vacancies further lead to improved CO2 conversion. As a result, an effective synergy between the active Ni sites and surface oxygen vacancies on In2O3 causes a superior catalytic performance for CO2 hydrogenation with high methanol selectivity. Carbon monoxide is the only by product detected. The formation of methane can be ignored. When the reaction temperature is lower than 225 °C, the selectivity of methanol is 100%. It is higher than 64% at the temperature range between 225 °C and 275 °C. The methanol selectivity is still higher than 54% at 300 °C with a CO2 conversion of 18.47% and a methanol yield of 0.55 gMeOH gcat−1 h−1 (at 5 MPa). The activity of Ni/In2O3 is higher than most of the reported In2O3-based catalysts.

Summary Ideal heterogeneous metal hydrogenation catalysts are featured by simultaneously high activity, selectivity, and stability. Herein, we report a general yet powerful strategy to design and fabricate dual-active-sites Co@C core-shell nanoparticle for boosting selective hydrogenation of various N-heteroarenes. It can break the limitation of scaling relation on traditional metal surfaces, and thus afford unprecedentedly high selectivity, activity, and stability. Combining kinetics analysis and DFT calculations with multiple techniques directly unveil that the critical porous carbon shell with a pore size of 0.53 nm not only allows H2 diffusion to Co sites for activation and blocks accessibility of N-heteroarenes but also catalyzes hydrogenation of N-heteroarenes via hydrogen spillover from Co sites. In addition, the presence of surface/subsurface carbon at the Co sites shows high anti-sulfur poisoning and anti-oxidant capability. This work is valuable for guiding the design and manipulation of cost-effective and robust hydrogenation catalysts.

The silica (S0) was pretreated with slightly acidic (S1) or basic (S2) aqueous solutions of ammonium salts before using as a support to prepare Rh–Mn–Li catalyst for CO hydrogenation to C2 oxygenates. The results showed that the weak acidity of the modified silica stem from silanol groups where the number of free silanol groups increased as S0

Ni–La2O3 cermet hydrogen electrode having almost no ionic conductivity still exhibits excellent electrochemical performance owing to the hydrogen spillover process from high hydrogen adsorption capability on the La2O3 surface. In this work, we develop Ni–La2O3 cermet hydrogen electrode originating from the in-situ decomposition of the La2NiO4+δ(LNO) oxide, and then perform the electrochemical properties for quasi-symmetrical solid oxide fuel cells (Q-SSOFCs), which own YSZ electrolyte support wrapped GDC barrier layer. The area specific resistance (ASR) of LNO air electrode increases from 2.09 to 7.41 Ω cm2, with the temperature of decreasing from 800 to 600 °C. The electrochemical performances of Q-SSOFCs with Ni–La2O3 cermet hydrogen electrode and LNO air electrode are characterized, and the values of the peak power density and the electrode polarization resistance (Rp) of the symmetrical electrodes measured at 800 °C are 245.18 mW cm−2 and 0.61 Ω cm2. These results indicate that the hydrogen spillover process of Ni–La2O3 cermet hydrogen electrode can greatly promote the hydrogen oxidation reaction.

Serial difunctional catalysts supported on γ-Al2O3 and HY zeolite were synthesized and characterized systemically. The characterization results disclosed that hydrogen spillover existed in the NiMo and CoMo catalysts, and decreasing Ni/Mo and Co/Mo ratios could reduce hydrogen spillover. Meanwhile, the naphthalene hydrocracking behaviors over different catalysts were investigated and compared. The higher yield of cyclane for CoMo/AY catalysts demonstrated that hydrogen spillover could deeply hydrogenate naphthalene into cyclane. The combined catalysts of Ni/[email protected]/A, Ni/[email protected]/A and Ni/[email protected]/A showed relatively lower conversions of naphthalene but higher yields of valued

Optimizing kinetic barriers of ammonia synthesis to reduce the energy intensity has recently attracted significant research interest. The motivation for the research is to discover means by which a...

High-performance electrocatalysts for the hydrogen evolution reaction (HER) have an important role to play in the development of renewable energy. Despite the enormous efforts to find cheaper alternative materials, platinum remains the most efficient known HER electrocatalyst. Therefore, it is necessary to find ways to maximize Pt utilization in actual practical applications. Here we demonstrate a facile strategy for synthesizing RuCeO x -supported selectively loaded atomic Pt (0.49 wt.%) (denoted Pt/RuCeO x -PA) by photoactivation at ambient temperature and pressure. Due to the photoelectron transfer at the Mott-Schottky heterojunction in RuCeO x , Pt atoms became directionally embedded into the RuO 2 lattice. The resulting selectively loaded Pt-O-Ru moieties in Pt/RuCeO x -PA exhibit a stronger hydrogen spillover effect than Pt complexes randomly loaded by either chemical activation or thermal activation. As a result, Pt/RuCeO x -PA shows superior HER performance to the materials prepared by random loading and is even better than a commercial Pt/C catalyst with much higher Pt loading (20 wt.%) at high current densities (from 50-600 mA cm -2 ). The selective loading strategy employed in our work not only provides an effective approach for constructing controllable active sites in HER catalysts but should also be applicable in the fabrication of other atomic catalysts.

Hydrogen storage by spillover in porous carbon material (PCM) has achieved great success in experiments. During the past 20 years, a large number of theoretical works have been performed to explore the hydrogen spillover mechanism, look for high-performance hydrogen storage materials and high-efficiency catalysts. In this paper, we summarize and analyze the results of the past researches, and draw the following conclusions: (1) In PCM surface, the stability of chemisorbed H can be reached through phase nucleation process, which can be initiated in the vicinity of surface impurities or defects. (2) To achieve the 2020 U.S. Department of Energy (DOE) target, the PCM material used for hydrogen storage by spillover should have a sp2 carbon ratio greater than 0.43 and a surface area less than 3500 m2/g, which gives us an inspiration for exploring hydrogen spillover materials. (3) Due to a high barrier, the hydrogen spillover almost can not be initiated on pure PCM substrate at room temperature. By introducing the defects or impurities (e.g. holes, carbon bridges, oxygen functional groups, boron atoms and fluorine atoms), the spillover barriers can be reduced to a reasonable range. In addition, hydrogen atoms may also migrate in a gas phase. (4) According to our previous results of kinetic Monte Carlo simulations, there is a linear relationship between the reaction temperature and the migration barrier. The optimal barrier for the hydrogen spillover should be in the range of 0.60–0.88 eV. (5) Once the hydrogen atoms are chemically adsorbed on the carbon substrate, it is difficult to diffuse again due to the strong strength of C–H bond. Several theoretical diffusion mechanisms have been proposed. For example, the H atoms in physisorption state can diffuse freely on carbon surfaces with high mobility, using the shuttle gases (e.g. BH−4, H2O, HF and NH3) to make the migration thermodynamically possible and decrease the migration barrier, the H atoms diffuse inside the interlayer space of the bi- and tetralayer graphene, and introducing the impurities on the surface to facilitate the hydrogen diffusion. (6) The H desorption through the directly recombination or the reverse spillover is unlikely to occur at normal temperature. The Eley-Rideal reaction may be the only possible mechanism for desorption of the adsorbed H atoms in carbon substrate. Finally, we have made a prospect for further research works on hydrogen storage by spillover.

In this work, strontium tantalate (Sr2Ta2O7) nanowires were used for the first time as a support of ruthenium catalysts for ammonia synthesis. The highest ammonia synthesis activity of 1582 μmol g-1cat h-1 was observed with Ru/Sr2Ta2O7 catalysts prepared with molar ratio of Sr(OH)2/Ta2O5 at 4. After loading promoters, the ammonia synthesis activity was significantly improved to 4856, 5004 and 5038 μmol g-1cat h-1 for K-, Rb- and Cs- modified Ru/Sr2Ta2O7 catalysts. Characterization and kinetic experiments indicate that the improved ammonia synthesis rate of promoters-Ru/Sr2Ta2O7 catalysts was attributable to the combined effect of alleviated hydrogen poisoning through the promotion of hydrogen spillover from Ru species to support of Sr2Ta2O7 and enhanced activation of N2 due to increased electron density of Ru sites because of electron donation from introduced oxygen vacancies and promoters. The study not only clarifies the role of promoters in ammonia synthesis, but also provides an excellent Ru catalyst on Sr2Ta2O7 nanowires for ammonia synthesis.