High Hydrogen Selectivity Research Articles

Catalytic methane pyrolysis in molten MnCl2-KCl

Methane decomposition to produce molecular hydrogen and solid carbon was catalyzed by contact with molten KCl:MnCl2 mixtures in a bubble column reactor from 700 to 1050 °C. The apparent activation energy decreased from approximately 300 kJ/mole for pure KCl to 161 kJ/mole in a 67:33 mol % mixture of KCl:MnCl2. At 30% methane conversion, pyrolysis in the KCl:MnCl2 melt at 1050 °C had high hydrogen selectivity (˜99%) in comparison to pure molten KCl (˜90%), which was observed to produce multiple hydrocarbon co-products. The pyrolysis activity of the KCl:MnCl2 melt remained stable for over 30 h and produced a separable, highly graphitic carbon solid that accumulated at the surface of the higher-density salt melt.

Hydrogen production from sucrose via aqueous-phase reforming

Commercial sucrose was used to produce hydrogen in a combined approach of hydrogenation and aqueous phase reforming (APR). First a mixture of technical sorbitol/mannitol was produced by hydrogenating an aqueous solution of sucrose in a trickle bed reactor over 5 wt % Ru/C. The produced polyols were treated in a continuous reactor at 498 K and elevated pressure deploying a 2.5 wt % Pt/C catalyst to yield hydrogen. The highest hydrogen selectivity was 62%. No large differences were found when comparing a commercial available sorbitol to the technical sorbitol/mannitol mixture in terms of conversion levels and selectivity to the gas-phase products. This was accompanied by a similar distribution of products retained in the liquid phase. The efficiency of APR when utilizing Pt/C was found to be still insufficient for industrial implementation in terms of hydrogen production. Thus, additional efforts should be made to increase the obtained amounts of hydrogen per mole of converted sugar alcohols.

Flexible Hydrogen Sensor Using Ni-Zr Alloy Thin Film

A triple-layered PMMA/Ni64Zr36/PDMS hydrogen gas sensor using hydrogen permeable alloy and flexible polymer layers is fabricated through spin coating and DC-magnetron sputtering. PDMS(polydimethylsiloxane) is used as a flexible substrate and PMMA(polymethylmethacrylate) thin film is deposited onto the Ni64Zr36 alloy layer to give a high hydrogenselectivity to the sensor. The measured hydrogen sensing ability and response time of the fabricated sensor at high hydrogen concentration of 99.9 % show a 20 % change in electrical resistance, which is superior to conventional Pd-based hydrogen sensors, which are difficult to use in high hydrogen concentration environments. At a hydrogen concentration of 5 %, the resistance of electricity is about 1.4 %, which is an electrical resistance similar to that of the Pd77Ag23 sensor. Despite using low cost Ni64Zr36 alloy as the main sensing element, performance similar to that of existing Pd sensors is obtained in a highly concentrated hydrogen atmosphere. By improving the sensitivity of the hydrogen detection through optimization including of the thickness of each layer and the composition of Ni-Zr alloy thin film, the proposed Ni-Zr-based hydrogen sensor can replace Pd-based hydrogen sensors.

Revealing the Hydrogenation Performance of RuMo Phosphide for Chemoselective Reduction of Functionalized Aromatic Hydrocarbons

Bimetallic transition metal phosphide catalysts are promising materials for low-temperature, liquid-phase hydrogenation reactions. This work explores the chemoselective hydrogenation ability of RuMoP using various functionalized aromatic hydrocarbons to provide insight into how the functional groups compete for reduction on the surface of RuMoP. Using molecular hydrogen as the reductant, high selectivity (∼99%) to reduction of the substituent is achieved for the hydrogenation of electron withdrawing functionalities such as nitrobenzene, benzaldehyde, and benzophenone with RuMoP to yield aniline, benzyl alcohol, and diphenylmethanol, respectively. In contrast, aromatics with electron donating groups such as phenol, anisole, and toluene, show high ring hydrogenation selectivity (∼99%) to form cyclohexanol, methoxycyclohexane, and methyl cyclohexane, respectively, although the reaction proceeded slowly with RuMoP. Pyridine adsorption was studied via diffuse reflectance infrared Fourier transform spectroscopy...

Co and La supported on Zn-Hydrotalcite-derived material as efficient catalyst for ethanol steam reforming

Abstract Four samples of Zn-hydrotalcite containing different amounts of Co (5, 10, 20, and 30 wt%) have been synthesized and tested in the steam reforming of ethanol. The best results were obtained with the sample containing 20 wt% of Co (20CoHT), with a complete conversion of ethanol and yields to hydrogen close to the equilibrium (73 mol.%). The physicochemical characterization of the samples by DRX, BET area and TPR indicates that the excellent performance exhibited by the sample containing 20 wt% of Co is due to the higher percentage of reduced cobalt and lower crystallite size of metallic cobalt present in this sample (11 nm). Additional studies have been carried out to improve the stability of this catalytic material against deactivation by the incorporation of 1 wt% of La. Stability studies were carried out using an industrial alcoholic waste as feed. Deactivation after 24 h of reaction time was found lower for the catalyst containing La (20CoLaHT), confirming the positive effect of lanthanum on the catalytic stability. The results presented here show that it is possible to prepare a catalyst based on Co supported on Zn-hydrotalcite and promoted with La with improved ethanol conversion, high hydrogen selectivity, and high stability to produce hydrogen by the steam reforming of an industrial alcoholic waste without commercial value.

Preparation and characterization of palladium ceramic alumina membrane for hydrogen permeation

In this study, a tubular palladium membrane has been prepared by an electroless plating method using palladium II chloride as a precursor with the intent of not having a completely dense film since its application does not require high hydrogen selectivity. The support used was a 15 nm pore sized tubular ceramic alumina material that comprised of 77% alumina and 33% titania. It has dimensions of 7 mm inner and 10 mm outer diameters respectively. The catalyst was deposited on the outside tube surface using the electroless deposition process. The membrane was morphologically characterized using scanning electron microscopy/energy dispersive x-ray analysis (SEM/EDXA) and liquid nitrogen adsorption/desorption analysis (BET) to study the shape and nature of the palladium plating on the membrane. The catalytic membrane was then inserted into a tubular stainless-steel holder which was wrapped in heating tapes so as to enable the heating of the membrane in the reactor. The gases used for permeation tests comprised H2, N2, O2 and He. Permeation tests were out at 573 K and at pressure range between 0.05 and 1 barg. The results showed that hydrogen displayed a higher permeation when compared to other gases that permeated through the membrane and its diffusion is also thought to include solution diffusion through the dense portions of the palladium in addition to Knudsen, convective and molecular sieving mechanisms occurring through cracks and voids along the grain boundaries. While high hydrogen selectivity is critically important in connection with hydrogen purification for fuel cells and in catalytic membrane reactors used to increase the yield of thermodynamically limited reactions such as methane steam reforming and water–gas shift reactions whereby the effective and selective removal of the H2 produced from the reaction zone shifts the equilibrium, it is not so important in situations in which the membrane has catalytic activity such that it is possible to carryout the reaction in situations where the premixed reactants are forced-through the membrane on which the catalysts is attached. This type of catalytically active membranes is novel and has not been tested in gas-solid-liquid reactions and liquid-solid reactions before. With such a reactor configuration, it is possible to achieve good feed stream distribution and an optimal usage of the catalytic material. The preparation and characterization of such membrane catalysts has gained increased interest in the process industries because it can be adapted to carryout the chemical reactions if one of the reactants is present in low concentration and an optimal reactant distribution results in a better utilization of the active catalytic material. However, there are concerns in terms of the high cost of palladium membranes and research on how to fabricate membranes with a very low content of the palladium catalyst is still ongoing. Work is currently underway to deploy the Pd/Al2O3 membrane catalysts for the deoxygenating of water for downhole injection for pressure maintenance and in process applications.

Microstructure and application of alumina-supported Cu-based coating prepared by cold spray

Cold spray technology is a recently developed surface modification method, which is widely used in various fields including the catalyst industry. Owing to their low reaction temperature, high activity, and high hydrogen selectivity, Cu-based catalysts are widely used in methanol steam reforming for hydrogen production. Cold spray is an efficient method for fabricating supported Cu-based catalysts for hydrogen production. However, in the cold spray process, the feedstock powder shape significantly affects the coating formation. In this study, we used two types of feedstock powders (consisting of dendritic Cu and clustered Al2O3) with different morphologies for fabricating Cu and Al2O3 coatings by cold spray on an Al substrate. A Cu + Al2O3 composite coating was also prepared by the cold spray method. The microstructures of the Cu, Al2O3, and Cu + Al2O3 coatings were investigated before and after methanol steam reforming. All the three feedstock powders were successfully deposited on the Al substrate. The coatings formed using the Cu and Cu + Al2O3 feedstock powders were multilayered and highly porous. Only slight deformation was observed in the micro-spherical structure of the Cu particle branches. In the case of the composite coating, Al2O3 particles were broken into pieces and were non-uniformly distributed. The bonding strength between the coating and the substrate was strong enough. After the methanol steam reforming process, the quality of the composite coating improved; however, the Cu coating showed carbon deposition. In order to obtain high-quality coatings, special attention should be paid to the feedstock particle shape and deposition of easily broken feedstock materials. The microstructural investigation of such coatings can be useful for understanding their fabrication mechanism. The fabrication method used in this study can be used as a novel method for fabricating supported catalysts.

Highly selective conversion of CO2 to light olefins via Fischer-Tropsch synthesis over stable layered K–Fe–Ti catalysts

K–Fe–Ti layered metal oxides (LMO) were prepared using solid-state reaction followed by in situ reduction and applied in CO2 hydrogenation to light olefins via Fischer-Tropsch synthesis process. The results showed that the molar ratio of K/Fe/Ti had dramatic effects on the textural and structural properties of the LMO and the catalytic performance. Layered structure K–Fe–Ti exhibited high olefin selectivity and stability for CO2 hydrogenation. The light olefin selectivity reached approximately 60% with an olefin/paraffin value of 7.3 over 0.8K–2.4Fe–1.3Ti, and the exfoliated LMO through acid treatment was found to weaken the interaction between Fe and Ti. This enabled the reduction and activation of iron oxides easier to form iron carbide species and promoted a shift from the reverse water gas shift reaction regime to hydrocarbon synthesis regime, contributing to higher hydrocarbons while lower CO.

Gas-phase synthesis of morphology-controlled Pt nanoparticles and their impact on cinnamaldehyde hydrogenation

Pt nanoparticles of which morphology is controlled by gas-phase synthesis using carbon monoxide as a protective agent show high catalytic activity and selectivity for cinnamaldehyde hydrogenation.

Highly active and selective Cu-ZnO based catalyst for methanol and dimethyl ether synthesis via CO2 hydrogenation

Highly active and selective Cu-ZnO based catalysts with high BET surface areas and Cu surface areas were prepared using the co-precipitation method. The Cu-ZnO based catalysts were systematically characterized and studied for methanol synthesis. Bifunctional catalysts, composed of Cu-ZnO based catalysts and HZSM-5 were studied for one-step dimethyl ether (DME) synthesis via CO2 hydrogenation. The effects of catalyst preparation conditions, reaction temperature, and pressure on methanol and DME synthesis were investigated and the optimum reaction conditions were determined. The optimized catalyst showed a BET surface area of 128 m2/g and a Cu surface area of over 59.3 m2/g, and demonstrated a high catalytic activity for CO2 hydrogenation. A bifunctional catalyst, prepared by a synthesized Cu-ZnO catalyst and HZSM-5, showed a high DME selectivity in one-step CO2 hydrogenation and methanol dehydration. The high activity and selectivity of the catalysts were attributed to the microstructure of the catalysts, which can be greatly affected by the catalyst preparation process. A long-term stability test showed a considerable decrease in activity within the first 20 h; however, the CO2 conversion (21.4%) and DME selectivity (55.5%) were still very high after 100 h.

Poly(amic acid) salt‐mediated palladium and platinum nanoparticles as highly active and recyclable catalysts for hydrogenation of nitroarenes in water under ambient conditions

Development of highly active and recyclable catalysts for selective hydrogenation of nitroarenes to amines in water at room temperature is always a challenge in chemical industry. This study reports a facile in situ method for synthesis of ultrafine palladium and platinum nanoparticles (NPs) stabilized by poly (amic acid) salt (PAAS) and their potential as catalysts for hydrogenation of nitroarenes with sodium borohydride or molecular hydrogen as reductant in water at room temperature. In the reduction of 4‐nitrophenol to 4‐aminophenol by sodium borohydride, the activity parameters of PdNPs–PAAS and PtNPs–PAAS catalyst is 6.66 × 103 and 5.58 × 103 s−1 M−1 respectively. In the hydrogenation of diverse nitroarenes under atmospheric hydrogen pressure, PdNPs–PAAS shows high activity but poor selectivity toward desired amines in some cases, while PtNPs–PAAS shows both high activity and high selectivity for selective hydrogenation of nitroarenes to corresponding anilines. The high efficiency of nanocatalyst is due to the quasi‐homogeneous dispersion of metal NPs and synergistic effects between metal NPs and PAAS. In addition, nanocatalyst can be easily recovered with pH‐sensibility of PAAS and reused at least six times without significant loss of catalytic activities.

Catalytic Performance and Characterization of Ni-Co Bi-Metallic Catalysts in n-Decane Steam Reforming: Effects of Co Addition

Co-Ni bi-metallic catalysts supported on Ce-Al2O3 (CA) were prepared with different Co ratios, and the catalytic behaviors were assessed in the n-decane steam reforming reaction with the purpose of obtaining high H2 yield with lower inactivation by carbon deposition. Physicochemical characteristics studies, involving N2 adsorption-desorption, X-ray diffraction (XRD), H2-temperature-programmed reduction (H2-TPR), NH3-temperature-programmed desorption (NH3-TPD), SEM-energy dispersive spectrometer (EDS), and transmission electron microscope (TEM)/HRTEM, were performed to reveal the textural, structural and morphological properties of the catalysts. Activity test indicated that the addition of moderate Co can improve the hydrogen selectivity and anti-coking ability compared with the mono-Ni/Ce-Al2O3 contrast catalyst. In addition, 12% Co showed the best catalytic activity in the series Co-Ni/Ce-Al2O3 catalysts. The results of catalysts characterizations of XRD and N2 adsorption-desorption manifesting the metal-support interactions were significantly enhanced, and there was obvious synergistic effect between Ni and Co. Moreover, the introduction of 12% Co and 6% Ni did not exceed the monolayer saturation capacity of the Ce-Al2O3 support. Finally, 6 h stability test for the optimal catalyst 12%Co-Ni/Ce-Al2O3 demonstrated that the catalyst has good long-term stability to provide high hydrogen selectivity, as well as good resistance to coke deposition.

Aqueous-phase reforming of Fischer-Tropsch alcohols over nickel-based catalysts to produce hydrogen: Product distribution and reaction pathways

Catalytic aqueous-phase reforming (APR) can be applied to process the organic compounds in the water fractions derived from the Fischer-Tropsch (FT) synthesis. This work aimed at finding an active nickel-based catalyst to convert organic compounds typically found in FT-derived waters, such as alcohols, into hydrogen. In addition, this work aimed at proposing potential reaction pathways that explain the product distribution resulting from the APR of C1–C3 alcohols. Solutions with 5% mass fraction of either methanol, ethanol, propan-1-ol or propan-2-ol in water were processed in APR at 230 °C and 3.2 MPa over different nickel-based catalysts in a continuous packed-bed reactor. Methanol was successfully reformed into hydrogen and carbon monoxide with conversions up to 60%. The conversion of C2–C3 alcohols achieved values in the range of 12% to 55%. The results obtained in the APR of C2–C3 alcohols suggest that in addition to reforming to hydrogen and carbon monoxide, the alcohols underwent dehydrogenation and decarbonylation. The most stable catalyst, nickel-copper supported on ceria-zirconia, reached feedstock conversions between 20% and 60% and high hydrogen selectivity. Monometallic nickel supported on ceria-zirconia catalysts reached higher H2 yields; however, the yield of side products, such as alkanes, was also higher over the monometallic catalysts. Accordingly, ceria-zirconia nickel-based supported catalysts constitute suitable candidates to process the alcohols in the water fractions derived from the FT synthesis.

C−C Bonds Cleavage of Biomass‐Derived Glycerol to Methane and Ethylene Glycol in Aqueous Phase Over Highly Dispersed Ru‐Based Catalysts

AbstractAn alternative method for the conversion of crude glycerol was proposed to produce renewable energy methane and high‐value chemical ethylene glycol through preferential cleavage of C−C bonds, catalyzed by highly dispersed Ru‐based catalysts prepared by carbothermal reduction. It was found that the Ru particles size could be tuned by adjusting the reduction temperature, and the size firstly decreased then increased with raising of the temperature of carbothermal reduction. This resulted in the opposite tendency of catalytic performance against the Ru particle sizes in hydrogenolysis of glycerol, in which the glycerol conversion and yield of C−C bond cleavage increased firstly and then decreased. Ru catalysts carbothermal reduced at 450 °C possessed highly dispersed Ru nanoparticles with uniform particle sizes about 1.0 nm that showed high hydrogenation activity and selectivity of C−C bond cleavage as well as good stability that could be recycled in aqueous phase hydrogenolysis of glycerol.

Pt/CeO2@MOF Core@Shell Nanoreactor for Selective Hydrogenation of Furfural via the Channel Screening Effect

Designing metal–organic framework (MOF)-encapsulated hybrid catalysts is considered as an effective way to realize catalytic selectivity because of advantages related to the unique channels of MOF. Here, a sodium polystyrenesulfonate (PSS)-induced, microwave-assisted route was developed to controllably construct Pt/CeO2@MOF core@shell hybrids. Using PSS as a modifying agent and followed by microwave assistance, MOFs could be continuously grown in an oriented manner on Pt/CeO2 nanospheres. The obtained Pt-CeO2@UIO-66-NH2 exhibited high conversion (99.3%) with high selectivity (>99%) for selective hydrogenation of furfural to furfuryl alcohol. It showed that the CeO2 would promote the catalytic activity, whereas the size confinement effect of the UIO-66-NH2 channels can enhance the catalytic selectivity. This work highlights a useful strategy toward the universal synthesis of highly active, stable, and selective catalysts for further utilization.

Highly Loaded and Dispersed Ni2P/Al2O3 Catalyst with High Selectivity for Hydrogenation of Acetophenone

Highly loaded and dispersed Ni2P/Al2O3 catalyst was prepared by the phosphidation of Ni/Al2O3 catalyst with Ni loading of 80 wt.% in liquid phase and compared with the Ni/Al2O3 catalyst for the hydrogenation of acetophenone. X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) etc. were used to characterize the textural and structural properties of the prepared catalysts. It was found that the Ni/Al2O3 and Ni2P/Al2O3 catalyst possessed high surface area, loading and dispersion. The Ni/Al2O3 catalyst had higher apparent activity while the Ni2P/Al2O3 catalyst had higher intrinsic activity for the hydrogenation of acetophenone (AP). Remarkably, the Ni2P/Al2O3 catalyst exhibited high selectivity to 1-phenylethanol, due to repulsion of the phosphorous (Pδ−) for phenyl group and attraction of the nickel (Niδ+) for oxygen atom of carbonyl group, leading to preferential hydrogenation of carbonyl group in acetophenone. The effect of the particle size of the catalyst on the chemical selectivity might be another reason for high selectivity on the Ni2P/Al2O3 catalyst.

Preparation of MOF Confined Ag Nanoparticles for the Highly Active, Size Selective Hydrogenation of Olefins

AbstractCatalysts with both high activity and good selectivity for hydrogenation of olefins to alkanes are of interest. Herein, MOF confined ultrafine Ag NPs (Ag@HKUST‐1) were synthesized by double‐solvent approach using HKUST‐1 as the template and support. HKUST‐1 with narrow cage size distribution (0.5 to 0.9 nm) confined the growth of Ag NPs, while the uniform pores prohibited the entrance of olefins with the molecular size lager than 5.0 Å, which endow the Ag@HKUST‐1 with high catalytic activity and size selectivity for hydrogenation reaction. The hydrogenation of eight kinds of olefins with different molecular size (1‐hexene, cyclohexene, 1‐octene, cyclooctene, styrene, 1‐decene, 1, 1‐diphenylethylene, and 1‐dodecene) catalyzed by Ag@HKUST‐1 confirmed this hypothesis. The olefins with molecular smaller than 5.0 Å were efficiently converted to the corresponding alkanes, whereas those greater than 5.0 Å exhibited extremely low conversation. The catalyst also exhibited high recycle stability in the hydrogenation of styrene.

Synthesis of Pd/SiO2 Catalysts in Various HCl Concentrations for Selective NBR Hydrogenation: Effects of H+ and Cl- Concentrations and Electrostatic Interactions.

A series of silica supported Pd (Pd/SiO2) catalysts were prepared in various HCl concentrations (CHCl) of the impregnation solution with different electrostatic interactions between Pd precursor and support, and their catalytic properties were evaluated by the selective hydrogenation of nitrile butadiene rubber (NBR). The results show that with the CHCl increasing from 0.1 to 5 M, the particle size of Pd nanoparticles dramatically decreases from 24.2 to 5.1 nm and stabilizes at ∼5 nm when CHCl is higher than 2 M. Using the catalysts prepared with a high CHCl (>2 M), an excellent hydrogenation degree (HD) of ∼94% with 100% selectivity to C=C can be acquired under mild conditions. Interestingly, the HD could be remarkably increased from 65 to 92% by increasing only CCl– from 0.1 to 2 M with the addition of NaCl while keeping CH+ at 0.1 M. This is because PdCl42– is the predominant existing form of precursor at high CCl–, which has a strong electrostatic attraction with the positively charged support favorable for the formation of small-sized Pd nanoparticles over silica. Notably, Pd leaching behavior during the hydrogenation reaction is closely related to CH+, and the higher the CH+, the less Pd residues are detected in the hydrogenated NBR. Our contribution is to provide a facile strategy to synthesize effective and stable Pd/SiO2 catalysts via adjusting the electrostatic interaction, which exhibits a high activity and selectivity for NBR hydrogenation.

An ordinary nickel catalyst becomes completely selective for partial hydrogenation of 1,3-butadiene when coated with tributyl(methyl)phosphonium methyl sulfate

Performance of an ordinary supported nickel catalyst was tuned to reach an almost complete selectivity for partial hydrogenation of 1,3-butadiene by coating it with a phosphonium-type ionic liquid (IL), tributyl(methyl)phosphonium methyl sulfate, [P4441][MeSO4]. Thanks to high chemical and thermal stability of [P4441][MeSO4], the reaction conditions could be pre-optimized for high partial hydrogenation performance before the deposition of the IL coating. When the catalyst was coated with IL, it provided a total butene selectivity of 99.5 ± 0.2%, a record high partial hydrogenation selectivity ever reported for a nickel-based catalyst. X-ray photoelectron spectroscopy results illustrated that the IL donates electrons to nickel sites and makes them selective for partial hydrogenation. The conductor like screening model for realistic solvents (COSMO-RS) calculations indicated that the IL coating also exerts a filter effect, which helps to maintain this high partial hydrogenation selectivity at all conversion levels.

Catalytic performances of Ni and Cu impregnated MCM-41 and Zr-MCM-41 for hydrogen production through steam reforming of acetic acid

A new mesoporous catalyst support material was synthesized by incorporation of zirconia into the structure of MCM-41 through a one-pot procedure. Catalytic performances of MCM-41 and Zr incorporated MCM-41 (25Zr-MCM-41) supported Ni or Cu catalysts were investigated in steam reforming of acetic acid reaction, at 750 °C. Some deformation in the ordered pore structure of MCM-41 was observed as a result of Zr incorporation. The activity test results showed that the catalytic performances of the zirconia incorporated MCM-41 were more stable than the MCM-41 supported materials. The catalysts containing 5% and 10% Ni gave highly promising results to achieve high hydrogen selectivity. However, the performance of the catalysts containing 5% Ni was more stable. Comparison of performances of Cu and Ni based catalysts showed that Cu was not a good catalyst for the steam reforming reaction of acetic acid. In the presence of copper, mainly decarboxylation reaction of acetic acid took place, yielding large quantities of methane. Results proved that, 5% Ni impregnated 25Zr-MCM-41 was a highly promising catalytic material for hydrogen production through steam reforming of acetic acid.