Hydrogen Spillover Effect Research Articles

Change in the gas sensing mechanism and improved sensing response on ion-irradiated palladium-graphene oxide nanocomposite

In this study, we synthesized Pd-graphene oxide (Pd-GO) nanocomposite layers on SiO2/Si substrates using chemical method. Pd-GO layers were treated with swift heavy ion irradiation (100 MeV Ag ions, 1013 ions/cm2). The structural properties of the pristine as well as the ion irradiated samples were investigated using synchrotron grazing incidence x-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) techniques. XRD shows peaks corresponding to Pd (FCC, space group-Fd-3m), GO and synthetic graphite. The relative graphite peak intensities increased after ion irradiation, indicating reduction of GO. The sensor responses of nanocomposite layers towards exposure of 35 ppm H2 at 100 °C, were measured for several cycles. Ion-irradiated Pd-GO samples show enhancement in the sensing response of H2 gas by about 24% and with lower recovery times (25%), as compared to pristine Pd-GO nanocomposite samples. The change in type of conductivity from p-type gas sensing layer in pristine nanocomposite to n-type conductivity, along with an increase in conductivity (about 500 times) in ion irradiated samples were observed. The change in type of conductivity on ion-irradiation is attributed to the reduction of GO layer and the changes in conductivity on hydrogen exposure is explained due to hydrogen spill-over effect in the two-component system. The improvement in sensitivity upon ion-irradiation was due to the increase in concentration of structural defects due to electronic energy loss, as studied by SRIM simulation. This study points towards using ion induced electronic energy loss as a new tool for varying the gas sensing properties of GO based sensors.

Pd-modified CuO-ZnO-Al2O3 catalysts via mixed-phases-containing precursor for methanol synthesis from CO2 hydrogenation under mild conditions

A series of palladium-modified (Pd-modified) CuO-ZnO-Al2O3 (CZA) catalysts with various Pd loadings (0.3 wt% to 2.4 wt%) were prepared using the wetness impregnation method, on two CZA supports with different structures that are CZA-aged precursor composed of a mixture of zincian-malachite and hydrotalcite-like phases (CZA-zH), and CuO-ZnO-Al2O3 metal oxide nanoparticles (CZA-MO). Enhancement on catalytic activity can be observed on both Pd-modified CZA catalysts in a temperature range of 180–240 °C for methanol synthesis via CO2 hydrogenation. Pd/CZA-zH catalysts exhibited a more efficient and stable production of methanol at a relatively low reaction temperature of 180 °C for 100 hrs of reaction. The improvement of activity is mainly ascribed to a higher surface area and abundant oxygen-containing functional groups (e.g., –OH) of CZA-zH support, which is beneficial for better adsorption and distribution of Pd promoter. Hydrogen temperature programmed reduction and X-ray photoelectron spectroscopy results demonstrated a better interaction between Pd and Cu on Pd/CZA-zH catalysts via enhanced reducibility of CuO, and peak shift of Cu to a lower binding energy. The difference in the efficient utilization of hydrogen spillover effect of Pd promoter over two CZA supports resulted in the different performances for methanol synthesis under mild reaction conditions.

Correlating O-Vacancy and Hydrogen Spillover with Activity and Selectivity in Furfural Hydrogenation Using Nanocatalysts Comprised of Ru Nanoparticles Supported on TiO2–SiO2

The nanoengineering of efficient and stable nanocatalysts is highly desired for sustainable biomass valorization toward the selective hydrogenation of furfural. The interaction of supports with metallic nanoparticles and oxygen vacancies has a significant role in the catalytic activity of oxide nanocatalysts. Here, by combining density functional theory (DFT) calculations and catalytic experimental data, we demonstrated that the presence of TiO2 in Ru–SiO2 catalysts might allow an association between oxygen vacancies and the hydrogen spillover effect. Specifically, Ru–TiO2–SiO2 and Ru–SiO2 nanocatalysts displayed improved activities and selectivities toward the reaction mentioned above. The nanomaterials were prepared by a simple, versatile, and single-step modified sol–gel process build upon two different stabilizing agents (P123 and CTAB), which afforded entirely covered surfaces of TiO2–SiO2 and SiO2 supports with uniform small Ru nanoparticles generated in situ. The Ru-TSdc nanocatalyst displayed several interesting promising nanoscale features for hydrogenation of furfural: (i) uniform distribution of Ru, Ti, and Si elements over the entire catalyst surface, (ii) deposition of small Ru nanoparticles with no significant particle agglomeration, (iii) facilitated hydrogen spillover from Ru NPs to the TiO2 support, and (iv) a significant amount of oxygen vacancies at the nanoparticle surface. For these reasons, the Ru-TSdc sample afforded the optimal performance toward the selective hydrogenation of furfural (up to 99% of selectivity), maintaining good conversions in certain reaction conditions. This work demonstrates how the catalytic activity of metallic nanoparticles could be improved by the structural addition of a reducible oxide, leading to more efficient inorganic supports and for preparing nanocatalysts.

Boosting Polyethylene Hydrogenolysis Performance of Ru-CeO2 Catalysts by Finely Regulating the Ru Sizes.

Hydrogenolysis is an effective method for converting polyolefins into high-value chemicals. For the supported catalysts commonly used, the size of active metals is of great importance. In this study, it is discovered that the activity of CeO2 -supported Ru single atom, nanocluster, and nanoparticle catalysts shows a volcanic trend in low-density polyethylene (LDPE) hydrogenolysis. Compared with CeO2 supported Ru single atoms and nanoparticles, CeO2 -supported Ru nanoclusters possess the highest conversion efficiency, as well as the best selectivity toward liquid alkanes. Through comprehensive investigations, the metal-support interactions (MSI) and hydrogen spillover effect are revealed as the two key factors in the reaction. On the one hand, the MSI is strongly related to the Ru surface states and the more electronegative Ru centers are beneficial to the activation of CH and CC bonds. On the other hand, the hydrogen spillover capability directly affects the affinity of catalysts and active H atoms, and increasing this affinity is advantageous to the hydrogenation of alkane species. Decreasing the Ru sizes can promote the MSI, but it can also reduce the hydrogen spillover effect. Therefore, only when the two effects achieve a balance, as is the case in CeO2 -supported Ru nanoclusters, can the hydrogenolysis activity be promoted to the optimal value.

Gamma-ray-irradiated construction of CuCo-based nanocomposites for attractive hydrogen production and tandem hydrogenation

Nitroarenes are important chemicals but display toxity to environment and organisms. In the present work, non-precious bicomponent CuCo-based nanocomposites (CuCo2O4/CuO) prepared with the aid of gamma(γ)-ray-irradiation were utilized for hydrogen production from ammonia borane (AB) hydrolysis and tandem hydrogenation of nitroarenes. The γ-ray-irradiation remarkably boosted the catalytic performance for the AB dehydrogenation and the hydrogenation of nitroarenes. Hydrogen generation rate (HGR) for the CuCo2O4/CuO catalyst reached 856.3 mL min−1·gcat−1, which was approximately two-fold than that of the catalyst prepared by conventional method (only 397.1 mL min−1·gcat−1). Meanwhile, this irradiation-induced catalyst also showed excellent performance for the hydrogenation of screened nitroarenes with 100% yield of the corresponding amines. The CuCo2O4/CuO catalyst exhibited high reusability with ∼90% remained activity of the initial one after six runs. The bicomponent CuCo2O4/CuO exhibited positive hydrogen spillover and synergistic effects contributing to the considerable activity improvement, which is beneficial to the detoxication, conversion and utilization of poison nitroarenes.

Improving the Efficiency of Hydrogen Spillover by an Organic Molecular Decoration Strategy for Enhanced Catalytic Hydrogenation Performance

Hydrogen migration from metal particles to the support, known as hydrogen spillover, has provided insights for designing highly efficient catalysts in catalytic processes involving hydrogen. A facile and controllable strategy is highly desired to achieve an effective hydrogen spillover effect on nonreducible oxides for catalytic performance optimization and clarifying the catalytic function of hydrogen spillover. Here, we provide an organic molecular decoration (OMD) strategy obtained by the molecular layer deposition-like pulse method for facilitating hydrogen spillover over the nonreducible silica support. After decorating with the fluoroalkylsilane (FAS) molecular layer, the hydrogen spillover effect over the catalysts (xFAS-Pt/SBA-15) is greatly enhanced due to the presence of carbonaceous species compared with the original Pt/SBA-15. The amount of hydrogen spillover can also be precisely regulated by controlling the FAS pulse number. For cinnamaldehyde hydrogenation, xFAS-Pt/SBA-15 presents superior catalytic performance versus its untreated counterpart and the sample decorated via the traditional method. Also, the catalytic activity varies based on the FAS pulse number, showing a linear correlation with the amount of hydrogen spillover. The altered adsorption behavior of the reactant plays an important role in the hydrogenation selectivity. This facile OMD strategy for efficient hydrogen spillover is general and may have potential applications in many heterogeneous reactions.

Constructing hierarchical structures of Pd catalysts to realize reaction pathway regulation of furfural hydroconversion

The technique of controlling nanoscale features precisely has been exploited to develop and improve bifunctional catalysts, which are important in the hydroconversion of furfural to high-value chemicals. Such bifunctional hydroconversion catalysts consist of metal sites and acid sites, and the intimacy extent of both active sites dictates the catalytic performance. In-depth exploration of the intimacy extent has been long limited by the lack of material synthesis and characterization method with nanometer precision. Herein, hierarchical catalytic structures with the spatial separation of Pd and acid sites were constructed by the multistep deposition strategy, wherein Pd was confined on defective CeO2 nanoclusters, which were dispersed on high-surface-area SiO2 with the strong acidity. The intimacy extent of Pd and acid sites in hierarchical catalytic structures of Pd/CeO2/SiO2 can be modulated by adjusting the CeO2 content, which leads to the aqueous-phase hydrogenation of furfural following a unique treble-site mechanism. The perpendicular adsorption of furfural on enriched oxygen vacancies of Pd/CeO2 contributes to the selective hydrogenation of the carbonyl group, and then the formed furfuryl alcohol undergoes the acid-catalyzed rearrangement of furan rings on SiO2 through the cooperative effect of acid sites and hydrogen spillover to give cyclopentanone. Meanwhile, the asynchronous catalysis effectively hinders the furan ring hydrogenation to tetrahydrofurfuryl alcohol by spatially separating Pd from the SiO2 surface. The superior catalytic performance is obtained on Pd/CeO2/SiO2-10 with a furfural conversion of 93% and cyclopentanone selectivity of 84%. We anticipate that the strategy of constructing hierarchical catalytic structures demonstrated here to spatially organize different active sites at the nanoscale will boost the further development of multifunctional catalysts.

Boron-induced controlled synthesis of Co-nano particles over Bx(CN)y matrix for CO hydrogenation in aqueous media

Bx(CN)y supported cobalt nanoparticles have been synthesized by regulating the ratios of melamine and boric acid precursors. The carbonization step is adequate to generate the desired controlled-sized cobalt particles at an auto-reduced state that can eliminate the requirement of promotors (e.g., Pt) for the hydrogen-spillover effect. The presence of nitrogen in support enhances the dispersion of cobalt particles by providing sites for cobalt to nucleate and grow due to the interaction between cobalt and Π electrons from the sp2-N center. Boron in the catalyst system significantly stabilizes the catalyst, thus improving its lifetime. However, the excess of boron promotes the aggregation of cobalt particles; therefore, optimal boron loading is preferable. Moreover, the binding energy calculation of Co6 over the B-doped and undoped C3N4 surface computed through DFT studies shows a reduction in metal-support interaction with the addition of boron, which leads to the aggregation of the cobalt particles with high boron. Overall, the catalyst with the optimized boron and nitrogen-containing support-stabilized cobalt particles is highly efficient in the aqueous phase Fischer-Tropsch synthesis.

Boosting photocatalytic ammonia synthesis performance over OVs-Rich Ru/W18O49: Insights into the roles of oxygen vacancies in enhanced hydrogen spillover effect

Synergistic water activation and nitrogen reduction process is significant to the photocatalytic ammonia synthesis reaction, in which the obtainment of active hydrogen (H*) from H2O dissociation and then transfer to N2 activation site is essential. Herein, the oxygen vacancies (OVs) enhanced hydrogen spillover is used to increase the H* transfer between the H2O activation site (Ru) and the N2 activation site (OVs-rich W18O49). Results shown that the OVs-rich Ru/W18O49 achieves high activity for NH3 production with a yield of 222.75 µmol‧g−1‧h−1, which is 5.60 folds of the OVs-deficient Ru/W18O49. Control experiments, characterization, and theoretical calculation made it clear that OVs played crucial roles in enhancing the hydrogen spillover by modifying the support's Gibbs free energy for hydrogen adsorption and lowering the barrier of H* migration. Finally, the detail mechanism was explained from a new perspective. This strategy may provide new insights for other hydrogenation reactions under mild conditions.

NOx storage and reduction by H2 over highly dispersed Pt on Co1Mg2Al1Ox-LDO for stationary applications: A transient kinetic study

The performance of a highly dispersed Pt/Co1Mg2Al1Ox-LDO catalyst towards NOx-storage and reduction by H2 for NOx control in stationary applications was investigated under forced feed composition cycling (“swing-reactor” system). The influence of 7 vol% CO2 and 5 vol% H2O in the NO-containing and H2-containing feeds on the dynamic evolution of adsorbed NOx-s and their reduction performance (conversion and N2-selectvity) were determined in the 200–400 oC range. The effects of catalyst pretreatment with 20 or 50 ppm SO2/He gas mixture on its NOx-s storage and reduction by hydrogen dynamics were also investigated. Reduction of NOx-s formed on the support involves a hydrogen spillover effect from Pt to the metal-support interface and support NOx-s sites. A very stable NSR performance was obtained at 350 oC for 2 h of successive NOx-adsorption (3 min)/reduction by H2 (1 min) steps. The nature of active and inactive NOx-s in H2 was probed by in-situ DRIFTS.

Effect of MoO3 on Pd nanoparticles for efficient formic acid electrooxidation

Palladium is a promising formic acid electro-oxidation (FAO) catalyst due to its higher initial activity than platinum. However, suffering from the adsorption of hydrogen and CO-like species, the activity and stability of Pd are still unsatisfied. Herein, palladium nanoparticles deposited on carbon supported molybdenum trioxide (Pd–MoO3/C) is prepared with MoO3 as the promoter for FAO. X-ray photoelectron spectroscopy analysis proves the close contact between Pd and MoO3, which generates the hydrogen spillover effect and forms the Pd–Mo structure. The hydrogen spillover effect enhances the desorption of hydrogen from Pd and facilitates the FAO activity. Both the spillover effect and Pd–Mo structure contribute to the removal of COad and facilitate the durability and anti-CO poisoning ability of the catalyst. With the optimized ratio of MoO3 to carbon black, the Pd–MoO3/C-20 catalyst owns the best specific activity of 5.86 mA cm−2, which is 1.86 times of Pd/C.

Hydrogen Spillover‐Promoted Hydrogen Evolution onto Copper

AbstractCurrently, green hydrogen harvesting from electrochemical water splitting is overly reliant on noble metals with high catalytic activity but low natural abundance and high cost. As one of potential earth‐abundant alternatives, copper, however, displays a poor hydrogen evolving capability, mainly due to inherently a weak hydrogen binding energy (HBE). It poses a substantial restriction to metallic Cu alone serving as primary active sites for high‐performance hydrogen evolution. Thanks to the presence of hydrogen spillover that was often overlooked during the electrocatalysis, the hydrogen evolution in a nonacidic electrolyte can be accelerated by the recombination desorption of adsorbed hydrogen over Cu with a weak HBE. Here, we concisely highlighted this promotion effect of secondary active Cu on electrocatalytic hydrogen evolution and eagerly expected to extend hydrogen spillover effects to the advance of multi‐site electrocatalytic systems.

Hydrogen spillover effect – harnessing hydrogen evolution reaction from diverse carbon-based supports with a tungsten oxide catalyst

The phenomena of the hydrogen spillover mechanism on different carbon supports.

Pd-doped HKUST-1 MOFs for enhanced hydrogen storage: effect of hydrogen spillover.

Extensive research has been devoted to developing metal nanoparticle (NP) doped porous materials with large hydrogen storage capacity and high hydrogen release pressure at ambient temperature. The ultra-sound assisted double-solvent approach (DSA) was applied for sample synthesis. In this study, tiny Pd NPs are confined into the pore space of HKUST-1, affording Pd@HKUST-1-DS with minimizing the aggregation of Pd NPs and subsequently the formation of Pd NPs on the external surface of HKUST-1. The experimental data reveal that the obtained Pd NP doped Pd@HKUST-1-DS possessed an outstanding hydrogen storage capacity of 3.68 wt% (and 1.63 wt%) at 77 K and 0.2 MPa H2 (and 298 K and 18 MPa H2), in comparison with pristine HKUST-1 and impregnated Pd/HKUST-1-IM. It is found that the storage capacity variation is not only ascribed to the different textural properties of materials but is also illustrated by the hydrogen spillover induced by different electron transport from Pd to the pores of MOFs (Pd@HKUST-1-DS > Pd/HKUST-1-IM), based on X-ray photoelectron spectroscopy and temperature desorption spectra. Pd@HKUST-1-DS, featuring high specific surface area, uniform Pd NP dispersion and strong interaction of Pd with hydrogen in the confined pore spaces of the support, displays the high hydrogen storage capacity. This work highlights the influence of spillover caused by Pd electron transport on the hydrogen storage capacity of metal NPs/MOFs, which is governed by both physical and chemical adsorption.

Fabrication of Ru nanoclusters on Co-doped NiSe nanorods with efficient electrocatalytic activity towards alkaline hydrogen evolutionviahydrogen spillover effect

The hydrogen spillover strategy was demonstrated to enhance the HER activity of Ru in alkaline electrolytes through Co doping into NiSe. 1.5 wt% Ru–Ni0.85Co0.15Se/NF with a smaller |ΔΦ| value showed a superior HER performance and stability.

Hydrogen spillover in Pt5Ru1 nanoalloy decorated Ni3S2 enabling pH-universal electrocatalytic hydrogen evolution

Based on the hydrogen spillover effect, the binary ‘metal–support’ Ni3S2/Pt5Ru1 is in situ constructed on Ni foam for electrocatalytic hydrogen evolution.

Hydrogen spillover effects in the Fischer–Tropsch reaction over carbon nanotube supported cobalt catalysts

Support (CNTs) surface defect-induced hydrogen spillover significantly impacted the catalytic activity (turnover frequency, TOF) and methane selectivity evolution in cobalt-based Fischer–Tropsch synthesis.

Enhanced electrochemical hydrogen storage performance upon the Pt-Co nanoparticles decorated N-doped mesoporous carbon

Carbonaceous materials are proved to be the promising materials for storing hydrogen electrochemically. To enhance the performance, decorated Pt-Co bi-metallic nanoparticles onto the N-doped mesoporous carbon material were developed while Co enriched the capacity, and Pt was used to enhance the kinetic performance. Results showed that the hydrogen storage capacity of 2% Pt-Co@NMC material was over 360 mAh g−1 under a current density of 100 mA g−1, and the capacity retention was 53.6% under the 2000 mA g−1 rate over that at 100 mA g−1. Furthermore, it also carries low self-discharge and good cycling performance. First-principles calculations revealed that the adsorption of the H atom on the Pt (110) crystal plane is the most stable, which is mainly due to the hydrogen spillover effect to improve the kinetic performance of hydrogen intercalation.

Synergistic trimetallic Ni–Cu–Sn catalysts for efficient selective hydrogenation of phenylacetylene

Selective hydrogenation of phenylacetylene is the most effective way to remove a small amount of phenylacetylene from styrene, but it is still a challenge to develop catalysts with high activity and selectivity. Herein, a series of non-precious bimetallic Ni3M/SiO2 (M = Zn, Sn, Cd, Fe, Co, Cu, or Mo) and trimetallic Ni3Cu–Sn/SiO2 catalysts were prepared and applied to selective hydrogenation of phenylacetylene. A trade-off between activity and selectivity was observed on Ni3M/SiO2, where Ni3Cu/SiO2 showed the best hydrogenation activity because of the hydrogen spillover effect of the Ni–Cu alloy, while Ni3Sn/SiO2 exhibited the highest selectivity to styrene due to the active-site isolation effect of the Ni–Sn alloy. Impressively, trimetallic Ni3Cu–Sn/SiO2 offered superior catalytic performance (94 % styrene selectivity at >99 % phenylacetylene conversion) as compared to bimetallic catalysts, owing to the synergistic effect among Ni, Cu, and Sn. In the case of Cu and Sn co-doping, the hydrogen spillover on the Ni–Cu alloy was deeply suppressed by Sn, which enabled an effective modification of the geometric and electronic structures of Ni to favor styrene desorption. The hydrogenation activity of Ni3CuSn0.3/SiO2 can be readily enhanced by increasing the metal loading and further improved by elevating the reaction temperature and pressure, but meanwhile the high selectivity is little affected. This work demonstrates a multi-metal synergistic strategy to break the activity–selectivity trade-off of Ni-based bimetallic catalysts in the selective hydrogenation of alkynes.

Insights into the active sites of dual‐zone synergistic catalysts for semi‐hydrogenation under hydrogen spillover

AbstractA well‐defined catalyst with platinum (Pt) and gold (Au) encapsulated in micropore and mesopore of micro‐mesoporous zeolite (Pt‐Au/TMSN), respectively, was designed to investigate the original active sites of semi‐hydrogenation. Specifically, hydrogen molecules are dissociated on Pt nanoclusters (NCs) to form hydrogen atoms that migrate to the surfaces of TMSN zeolite and Au nanoparticles (NPs) through hydrogen spillover effect. The characterization and catalytic results demonstrate that the Au NPs and zeolite surface are both identified as the semi‐hydrogenation sites. Especially, the Au active site with low adsorption ability of alkene possesses preferable selectivity in the semi‐hydrogenation of phenylacetylene and 1,5‐cyclooctadiene. Noteworthy, the Pt‐Au/TMSN exhibits higher selectivity of phenylethylene and cyclooctene than Pt/TMSN, as well as higher turnover frequency than Au/MSN. This work creates an effective regulation strategy of active sites working with a tandem mechanism for improving the semi‐hydrogenation performance.