Hydrogen Spillover Effect Research Articles

Co–Pd/γ‐Al2O3 catalyst for heavy oil upgrading: Desorption kinetics, reducibility and catalytic activity

AbstractThe influence of Pd on a Co–Pd/γ‐Al2O3 heavy oil upgrading catalyst is investigated using different physicochemical and reactive Characterization techniques. Nitrogen adsorption isotherm analysis shows that the specific surface area and porosity of the support alumina is significantly decreased due to the blockage of the pores by the loaded cobalt species. The estimated activation energy of NH3 desorption is found to be less for Co–Pd/γ‐Al2O3 sample, which confirms improved acidity due to Pd. TPR experiments show that the reducibility of the catalyst is significantly improved with the presence of Pd. Higher metal dispersion and hydrogen spillover effects are the main reasons for the enhanced reducibility of the Pd promoted catalyst as revealed by the H2‐pulse chemisorptions study. When evaluated using VGO as feed stock, the Co–Pd/γ‐Al2O3 displayed superiority both in hydrodesulphurisation (HDS) and hydrocracking (HC) activities as compared to the unpromoted Co/γ‐Al2O3 catalyst. The coke deposition on the spent catalyst is also found to be low due to the Pd promotional effects. This is an encouraging result, given that higher hydrogenation activity of the catalyst can be achieved without compromising the cracking activity and sustained activity of the catalyst.

Autothermal reforming of low-sulfur diesel over bimetallic RhPt supported on Al2O3, CeO2–ZrO2, SiO2 and TiO2

The objective of this paper is to study and clarify the role of selected supports (both reducible and non-reducible) on the activity, selectivity and stability of RhPt-based catalyst for diesel reforming. Autothermal reforming (ATR) of low-sulfur diesel (S ∼6ppm, C/H ∼6.43 (w/w)), H2O/C ∼2.5, O2/C ∼0.49, was tested at bench scale to detect differences in activity for catalysts consisting of 1wt% Rh and 1wt% Pt supported on alumina, ceria–zirconia (17.5wt% ceria), silica and titania. Promoters in the form of MgO, Y2O3, La2O3, CeO2 and ZrO2, ranging from 4wt% to 10wt%, were also added onto the supports to detect differences in catalyst activity in terms of diesel conversion, CO2 selectivity, and hydrogen and ethylene production. All metals were added sequentially onto the support by the incipient wetness technique and washcoated on 400cpsi cordierite monolithic carriers with dimensions d=17.8mm, l=30.5mm.The product gas analysis, using FTIR and NDIR, showed that RhPt/CeO2–ZrO2 was found to be most active for ATR of diesel since a fuel conversion close to 98% was obtained. Furthermore, the catalyst activity of the unpromoted samples, in terms of diesel conversion, increased in the following order: RhPt/SiO2<RhPt/TiO2<RhPt/Al2O3<RhPt/CeO2–ZrO2. The addition of promoters was found to be insignificant as well as having a negative impact on the catalyst performance in most cases, except for the alumina-promoted sample. The addition of 10wt% La2O3 on RhPt/Al2O3 was found to enhance diesel conversion, hydrogen productivity as well as lower the ethylene concentration from 3700ppm to less than half that value. The latter observation was confirmed by O2-TPO analysis of aged powder samples where lower loads of coke were present than on the La-promoted sample.The morphology, surface and bulk properties of RhPt/CeO2–ZrO2 were closely examined in order to provide a possible correlation between the activity and characterization results. N2-BET analysis showed that the surface area of RhPt/CeO2–ZrO2 was ∼64m2/g, while the silica samples exhibited the highest area, ∼137–185m2/g. Hence, the difference in the surface areas was not enough to explain the trends observed in the activity measurements. XRD analysis of RhPt/CeO2–ZrO2 showed crystalline phases characteristic of zirconia, most likely tetragonal. Also, the diffractogram did not reveal any Rh or Pt peaks indicating that the noble metal particles are highly dispersed on the support. In contrast, peaks ascribed to metallic Pt (∼30–46nm) were clearly visible on the XRD patterns taken from all the other supported samples. H2-TPR analysis of RhPt/CeO2–ZrO2 showed reduction peaks ascribed to RhiOx species as well as a minor hydrogen spillover effect on the support to be present at T=120°C and 450°C, respectively. Also, the hydrogen consumption of the RhiOx species was the highest compared to the other supported RhPt samples. TEM analysis performed on fresh RhPt/CeO2–ZrO2 showed that the RhiOx and Pt particles were highly dispersed on the support, both with particle sizes in the vicinity of ∼5–15nm. Rh species was found on ceria and zirconia, while Pt was present mainly on the ceria layer possibly in the form of Pt–O–Ce bonds. H2-chemisorption analysis measured at T ∼40°C shows similar Rh dispersion results.To summarize, the higher activity results of RhPt/CeO2–ZrO2 for ATR of diesel, compared to other supported catalysts, may be ascribed to the higher reducibility of RhiOx species as well as the superior Rh and Pt dispersion. Also, the support contribution, in particular ceria, is believed to promote water gas-shift activities as well as reduce coke deposits on the catalyst surface.

Transition metal-decorated activated carbon catalysts for dehydrogenation of NaAlH 4

Dehydrogenation of NaAlH 4 can be greatly facilitated by activated carbon catalysts. The catalytic function can be further enhanced by decorating the carbon with Co, Ni, or Cu nanoparticles. The decomposition temperature was lowered by as much as 100 °C using a 3 wt.% Co or Ni-decorated activated carbon, comparable to a Ti-based catalyst, which were the most effective among the metals tested. The catalytic effect is likely due to a combination of hydrogen spillover effect, high contact area between carbon and the hydride, and confinement of the hydride as nano-sized domains in the pores of the carbon matrix. The catalysts were also effective in facilitating rehydrogenation of NaAlH 4 under moderate pressure (75.8 bar H 2) and low temperature (120 °C), when no rehydrogenation would occur without the catalyst. The fact that this new catalyst system is not specific to any hydride offers many potential applications.

Preparation of a Cu–Ru/carbon nanotube catalyst for hydrogenolysis of glycerol to 1,2-propanediol via hydrogen spillover

A Cu–Ru nanoparticle catalyst supported on carbon nanotubes was prepared by a chemical replacement reaction between Cu metal nanoparticles and Ru3+ cations. The as-prepared catalyst was characterized by X-ray diffraction, X-ray photoelectron spectroscopy, H2 and CO chemisorption, and transmission electron microscopy. The results showed that the highly dispersed Ru clusters were present on the external surface of the Cu particles. These tiny Ru clusters did not activate glycerol to carry its hydrogenolysis, but instead activated and generated active hydrogen, which was transferred to the Cu surface nearby viahydrogen spillover. The Cu–Ru catalyst exhibited selectivity for 1,2-propanediol that was as high as Cu metal, and much higher hydrogenolysis activity than pure Cu metal because of the hydrogen spillover effect, which benefited from the Ru clusters.

Ruthenium nanoparticles embedded in mesoporous carbon microfibers: preparation, characterization and catalytic properties in the hydrogenation of d-glucose

Ruthenium (Ru) nanoparticles dispersed in mesoporous carbon microfibers were prepared using alumina microfibers as the templates via a chemical vapour deposition (CVD) route. Characterized data showed that Ru nanoparticles were embedded in the mesoporous carbon matrix. The samples were found to possess a specific surface area as high as 750 m(2) g(-1), pore sizes in the range of 3-5 nm, lengths in the range of 5-10 μm, and a width of about 0.5 μm. The Ru catalysts displayed a remarkably high catalytic activity and an excellent stability in the hydrogenation of D-glucose. The observed good catalyst performance is attributed to the carbon microfiber morphology, unblocked mesoporous structure, and the hydrogen spillover effect induced by the unique surface contact between the Ru nanoparticles and the carbon. In addition, the incorporation of nitrogen significantly improved the catalytic performance due to the enhanced hydrogen adsorption, better wettability, and modified electronic properties of the Ru.

Room temperature sensing properties of networked GaN nanowire sensors to hydrogen enhanced by the Ga2Pd5 nanodot functionalization

Multiple-networked GaN nanowires with excellent sensing properties to hydrogen were realized by functionalizing their surfaces with Ga2Pd5-related nanodots. Compared to the bare-GaN nanowire sensors, functionalization improved the relative resistance responses by a factor of >50 at H2 concentrations ranging from 100 to 2000 ppm. At room temperature, the nanodot-functionalized GaN nanowire sensors exhibited a relative resistance response of 34.1% at 100 ppm H2. Interestingly, a shell layer was transformed mostly into Ga2Pd5-phased nanodots, which was confirmed by X-ray diffraction and transmission electron microscopy. The mechanisms responsible for the improvement induced by nanodot functionalization are proposed in terms of the hydrogen spillover effect.

Catalysis-spillover-membrane. III: The effect of hydrogen spillover on the palladium membrane reactor in the steam reforming reactions

In this paper, the effect of varying the distance between a palladium membrane and the steam reforming catalyst in a packed bed catalytic membrane reactor is studied. A set of the specially structured palladium membrane tube is prepared and used for the steam reforming reaction of n-hexane and of methanol. This specially designed palladium membrane structure has a long tube at the upstream-end of membrane tube, and it is electroplated with thin nickel or palladium film. This nickel or palladium plated metal surface serves as a bridge for the surface diffusion of the nascent hydrogen atoms over a 10 cm distance to the membrane surface for permeation out of the system after they are formed on the catalyst site and spillover from the catalyst surface to the diffusion bridge. As a result, the conversion level of steam reforming reaction is increased while byproduct formation of methane is suppressed. Furthermore, it is believed that the direct migration of the nascent hydrogen atom from the catalyst site to the membrane surface via direct spillover or via surface diffusion brings about a stronger positive contribution to the steam reforming reaction than does the vapor phase diffusion of the molecular hydrogen on the reaction. This extension tube allows the membrane and the catalyst section to operate under mutually optimized temperatures in a single reaction chamber while preserving high membrane efficiency; thus the use of this new membrane structure makes design of a membrane reactor more flexible to maximize mutual efficiency of catalyst and the membrane.

The enhancement effect of MoOx on Pd/C catalyst for the electrooxidation of formic acid

Molybdenum oxide (MoOx) was added to a Pd/C catalyst using a novel two-step procedure. The enhancement effect of MoOx on Pd/C catalyst for the electrooxidation of formic acid was verified by electrochemical experiments. Compared to the Pd/C catalyst, the experimental results showed that the addition of MoOx could significantly enhance the electrocatalytic performances for the electrooxidation of formic acid. Significant improvements in electrocatalytic activity and stability were primarily ascribed to the effect of MoOx on the Pd catalyst. In addition to the large specific surface area, the hydrogen spillover effect is speculated to have accelerated the electrooxidation rate of formic acid in the direct pathway.

Pt nanoparticles supported on WO3/C hybrid materials and their electrocatalytic activity for methanol electro-oxidation

A simple and novel method for the preparation of WO3/C is presented. This method includes the adsorption and decomposition of phosphotungstic acid (PWA) on carbon. For the purpose of comparison, WO3/C is also prepared by a conventional method using sodium tungstate as the precursor. These two WO3/C species are denoted as WO3/C-1 and WO3/C-2, respectively. It is shown from transmission electron microscopy (TEM) that the WO3 particles in WO3/C-1 present a more even distribution and smaller particle size than those in WO3/C-2. Pt particles dispersed on WO3/C-1 display the characteristic diffraction peaks of Pt in the face-centered cubic phase. Cyclic voltammetry and chronoamperometry show that the Pt–WO3/C-1 catalyst exhibits much better methanol oxidation activity than the Pt–WO3/C-2 and Pt/C catalysts. This significant improvement in catalytic performance may be attributed to the hydrogen spillover effect and the uniform distribution of Pt and WO3 particles.

Hydrogen Storage Behaviors of Ni-Loaded Activated Carbon Nanotubes

In this work, nickel (Ni)-loaded activated carbon nanotubes (ACNTs) were prepared for hydrogen storage applications. The process was conducted by chemical activation method at 900oC with KOH:CNTs ratios (4:1, g/g). And then, Ni-loaded ACNTs were also formulated to investigate the hydrogen storage characteristics as a function of Ni content. The microstructures of the Ni-loaded ACNTs were characterized by XRD and TEM measurements. The textural properties of the samples were analyzed using N2 adsorption isotherms at 77 K. The BET, D-R, and BJH equations were used to observe the specific surface areas, the micropore, and mesopore structures, respectively. The hydrogen storage capacity of the Ni-loaded ACNTs was measured at 298 K at a pressure of 100 bar. It was found that the hydrogen storage capacity of Ni-loaded ACNTs was enhanced in proportion to the Ni content, with Ni-5-ACNTs exhibiting the largest hydrogen storage capacity. Therefore, it could be concluded that the significantly created micropores on CNTs by chemical activation had an effect on hydrogen storage behaviors as well as the Ni particles played an important role in hydrogen storage characteristics due to the hydrogen spillover effect.

The selective hydrogenation of acetylene on palladium–carbon nanostructured catalysts

A novel carbon nanostructured material was produced using the electric arc ablation method. The product was purified using a combination of extraction, acid reflux and selective oxidation. The purified carbon nanostructured material (CNS) consisted of single-walled carbon nanotubes (SWNTs) with an average tube diameter of 1.3 nm, and interconnected, nanostructured and multiwalled globules. Catalysts containing 1 and 5% (m/m) Pd supported on the CNS were synthesized involving an activation step, followed by electroless plating of the Pd on the CNS. The Pd/CNS catalysts consisted of Pd particles with an average diameter of 6 nm highly dispersed on the CNS. The activity and selectivity of the 1 and 5% Pd/CNS catalysts towards the hydrogenation of acetylene were determined under different conditions of temperature and pressure. The results were compared to that obtained for reference catalysts, namely 1 and 5% Pd/Al 2O 3, and 1 and 5% Pd/activated carbon, under the same conditions. The Pd/CNS catalysts proved to have superior selectivity and activity, and formed less green oil and no detectable coke formation compared to the commercial catalysts under the experimental conditions. It is postulated that this was due to reduced hydrogen spillover and sintering effects and the different surface morphology of the Pd/CNS catalysts compared to the commercial products.

Hydrogen storage behaviors of platinum-supported multi-walled carbon nanotubes

In this work, the hydrogen storage behaviors of multi-walled carbon nanotubes (MWNTs) loaded by crystalline platinum (Pt) particles were studied. The microstructure of the Pt/MWNTs was characterized by X-ray diffraction and transmission electron microscopy. The pore structure and total pore volumes of the Pt/MWNTs were analyzed by N 2/77 K adsorption isotherms. The hydrogen storage capacity of the Pt/MWNTs was evaluated at 298 K and 100 bar. From the experimental results, it was found that Pt particles were homogeneously distributed on the MWNT surfaces. The amount of hydrogen storage capacity increased in proportion to the Pt content, with Pt-5/MWNTs exhibiting the largest hydrogen storage capacity. The superior amount of hydrogen storage was linked to an increase in the number of active sites and the optimum-controlled micropore volume for hydrogen adsorption due to the well-dispersed Pt particles. Therefore, it can be concluded that Pt particles play an important role in hydrogen storage characteristics due to the hydrogen spillover effect.

Neutron Scattering Methodology for Absolute Measurement of Room-Temperature Hydrogen Storage Capacity and Evidence for Spillover Effect in a Pt-Doped Activated Carbon

A neutron scattering methodology is proposed to simultaneously determine the total hydrogen adsorption, the excess hydrogen adsorption, and hydrogen gas confined in the porous sample. This method is capable of an absolute measurement of the hydrogen content without need for any calibration. It involves the least amount of corrections and is not likely to be affected by the instrumental factors compared to the traditional gravimetric and volumetric methods. We used this method to study the physisorption behavior at room-temperature (RT) of a Pt-doped activated carbon sample as a function of hydrogen pressure. This method will become a simple and important tool for solving various problems arising from the traditional measurements of RT hydrogen storage capacities. It can be combined with an in situ small-angle neutron scattering to study the hydrogen spillover effect in the kinetic adsorption process. Storage capacity and spatial distribution of the hydrogen adsorbed due to spillover are concurrently revealed.

Effect of Catalyst Size on Hydrogen Storage Capacity of Pt-Impregnated Active Carbon via Spillover

There are two regimes that exhibit two distinctive behaviors of spillover. The present study used small-angle X-ray scattering (SAXS) to measure size distribution of Pt nanoparticles in the bulk Pt-impregnated active carbon sample. The peak position of the size distribution as determined by SAXS turns out to be at ∼1 nm, which is rarely discussed in this field. SAXS technique is complementary to the other characterization methods. The experimental clue coming from SAXS measurement and our hydrogen storage capacity study shows that the impregnated Pt nanoparticles of ∼1 nm in size can enhance the hydrogen spillover effect. It can significantly increase the room temperature hydrogen uptake compared to currently studied similar systems. The mass loading of catalyst is not a critical factor. Tuning the pore-confined Pt sizes (<2 nm) in combination with an optimum activation method should play an effective role in further enhancement via the spillover effect.

Production of hydrogen via steam reforming of biofuels on Ni/CeO2–Al2O3 catalysts promoted by noble metals

Abstract The catalytic activity of Ni/CeO 2 –Al 2 O 3 catalysts modified with noble metals (Pt, Ir, Pd and Ru) was investigated for the steam reform of ethanol and glycerol. The catalysts were characterized by the following techniques: Energy-dispersive X-ray, BET, X-ray diffraction, temperature-programmed reduction, UV–vis diffuse reflectance spectroscopy and X-ray absorption near edge structure (XANES). The results showed that the formation of inactive nickel aluminate was prevented by the presence of CeO 2 dispersed on alumina. The promoting effect of noble metals included a decrease in the reduction temperatures of NiO species interacting with the support, due to the hydrogen spillover effect. It was seen that the addition of noble metal stabilized the Ni sites in the reduced state along the reforming reaction, increasing the ethanol and glycerol conversions and decreasing the coke formation. The higher catalytic performance for the ethanol steam reforming at 600 °C and glycerol steam reforming was obtained for the NiPd and NiPt catalysts, respectively, which presented an effluent gaseous mixture with the highest H 2 yield with reasonably low amounts of CO.

Catalytic Cracking of Heavy Olefins into Propylene, Ethylene and Other Light Olefins

Hybrid catalysts developed for the thermo-catalytic cracking of liquid hydrocarbons were found to be capable of cracking C4+ olefins into light olefins with very high combined yields of product ethylene and propylene (more than 60 wt%) and C2–C4 olefins (more than 80 wt%) at 610–640 °C, and also with a propylene/ethylene weight ratio being much higher than 2.4. The olefins tested were heavier than butenes such as 1-hexene, C10+ linear alpha-olefins (LAO) or a mixture of LAO. The hydrogen spillover effect promoted by the Ni bearing co-catalyst, contributed to significantly enhancing the product yield of light olefins and the on-stream stability of the hybrid catalyst.

A decade's study and developments of palladium membrane in Taiwan

Research on palladium membrane was started in 1995 by China Technology Consultants Institute (CTCI), Taiwan; there are now more than four groups engaging in various aspects of study and development of palladium membrane and Green Hydrotec Inc. is running fabrication and application of the membrane for commercial development. The author reviews recent discovery in the permeation of hydrogen mixture by palladium membrane in his group. Their main discoveries are (1) new method of preparing strong palladium membrane by electroplating, (2) a new method of measuring hydrogen permeation in the case of mixture to avoid changing hydrogen concentration along the membrane tube, (3) the perturbed hydrogen permeation in the permeation of hydrogen mixture with palladium membrane due to palladium lattice expansion during permeation, (4) the effect of hydrogen spillover on the catalytic membrane reactor to account for the rate enhancement and the hike of reaction conversion when a palladium membrane is incorporated into the catalytic reactor, and (5) production of hydrogen by a 3-in-1 membrane reactor.

Contribution of hydrogen spillover to the hydrogenation of naphthalene over diluted Pt/RHO catalysts

This paper presents the contribution of hydrogen spillover to the hydrogenation of naphthalene over Pt/RHO catalysts. Platinum supported on RHO zeolite was prepared by adding a Pt precursor to the synthesis gel of RHO zeolite. Pt/RHO catalysts were characterized by XRD, TEM, TPR and XPS. The hydrogenation activity was tested using 1-hexene, 1-cyclohexene and naphthalene as model compounds. XRD and TEM results indicated that incorporating Pt precursors into the synthesis gel did not affect the crystal structure and the morphology of the RHO zeolite. TPR, XPS and hydrogenation tests revealed that Pt particles were located in both RHO cages and intrazeolite spaces. In Pt/RHO containing lower levels of cesium, a small amount of Pt was also located on the external surface of the zeolite. The contribution of hydrogen spillover over hybrid Pt/RHO_H-Y zeolite catalysts was examined in naphthalene hydrogenation. Naphthalene conversion increased from 21% over a Pt/RHO catalyst to 91% over Pt/RHO diluted with H-Y zeolite, clearly demonstrating the positive effect of hydrogen spillover on the hydrogenation reaction.

Hydrogen production by steam reforming of ethanol over Ni-based catalysts promoted with noble metals

The catalytic activity of Ni/La 2O 3-Al 2O 3 catalysts modified with noble metals (Pt and Pd) was investigated in the steam reforming of ethanol. The catalysts were characterized by ICP, S BET, X-ray diffraction, temperature-programmed reduction, UV–vis diffuse reflectance spectroscopy and X-ray absorption fine structure (XANES). The results showed that the formation of inactive nickel aluminate was prevented by the presence of La 2O 3 dispersed on the alumina. The promoting effect of noble metals included a marked decrease in the reduction temperatures of NiO species interacting with the support, due to the hydrogen spillover effect, facilitating greatly the reduction of the promoted catalysts. It was seen that the addition of noble metal stabilized the Ni sites in the reduced state throughout the reaction, increasing ethanol conversion and decreasing coke formation, irrespective of the nature or loading of the noble metal.

O.272 Local hyperthermia in treatment of tumors of head and neck

The catalytic performance of Ni/TiO2 and Ni–Ir/TiO2 catalysts in the selective hydrogenation of cinnamaldehyde (CAL) has been investigated. The Ni–Ir/TiO2 presented higher activity than the Ni/TiO2. Here, we studied and gave some insights into the interaction between Ni and Ir species and the role of Ir using X-ray diffraction (XRD), transmission electron microscope (TEM), hydrogen temperature-programmed reduction (H2 TPR), hydrogen temperature-programmed desorption (H2 TPD), and X-ray photoelectron spectroscopy (XPS). The size of Ni particles on the Ni–Ir/TiO2 was 10.1 nm, smaller than that (12.7 nm) on the Ni/TiO2. The reducibility of Ni was improved by addition of a small amount of Ir, as confirmed with the H2 TPR analysis. The Ni–Ir/TiO2 could be reduced at a temperature of 352 °C, which is lower than the temperature for Ni/TiO2 (385 °C); moreover, a new reduction peak appeared at 240 °C due to the stronger interaction of Ni–Ir species, which was certified by XPS analysis. The H2 TPD results indicate that the hydrogen spillover effect may occur in Ni–Ir/TiO2. The electronic structure of the surface Ni atoms was modified upon addition of Ir, resulting in an enhanced activity of the Ni–Ir/TiO2 catalyst, about four times as high as that of the Ni/TiO2 catalyst.