High Hydrogen Selectivity Research Articles

Selective hydrogenation of 1,3-butadiene on platinum-copper alloys at the single-atom limit.

Platinum is ubiquitous in the production sectors of chemicals and fuels; however, its scarcity in nature and high price will limit future proliferation of platinum-catalysed reactions. One promising approach to conserve platinum involves understanding the smallest number of platinum atoms needed to catalyse a reaction, then designing catalysts with the minimal platinum ensembles. Here we design and test a new generation of platinum–copper nanoparticle catalysts for the selective hydrogenation of 1,3-butadiene,, an industrially important reaction. Isolated platinum atom geometries enable hydrogen activation and spillover but are incapable of C–C bond scission that leads to loss of selectivity and catalyst deactivation. γ-Alumina-supported single-atom alloy nanoparticle catalysts with <1 platinum atom per 100 copper atoms are found to exhibit high activity and selectivity for butadiene hydrogenation to butenes under mild conditions, demonstrating transferability from the model study to the catalytic reaction under practical conditions.

Effect of support on acetic acid decomposition over palladium catalysts

Acetic acid decomposition for hydrogen production was investigated on Pd/SiO2, Pd/Nb2O5, Pd/La2O3 and Pd/Fe2O3 catalysts. The conversion of acetic acid started at 673K and the products of the reaction were H2, CO, CH4, CO2, H2O and C2H4O. Pd/Fe2O3 was the most active catalyst for conversion of acetic acid and showed high hydrogen selectivity and good catalytic stability, followed by Pd/Nb2O5 and Pd/La2O3, whereas in the case of Pd/SiO2, there was not any H2 formation. The Pd/Fe2O3 catalysts presented reduced Pd–Fe and Pd0/Fe2Ox sites, producing complete conversion of acetic acid and a higher level of hydrogen selectivity (73%). Additionally, acetic acid adsorption on Pd/Fe2O3, Pd/Nb2O5 and Pd/La2O3 catalysts yielded the formation of acetate surface species. However, in the case of Pd/SiO2, there was molecular adsorption of acetic acid. During the reaction, there was formation of an ordered and disordered carbon mixture on Pd/La2O3, Pd/Nb2O5 and Pd/SiO2 catalysts, while carbon of a more ordered nature was produced on Pd/Fe2O3.

Pd–Cu catalysts from acetate complexes in liquid-phase diphenylacetylene hydrogenation

Properties of Pd–Cu/Al2O3 catalysts prepared using PdCu(CH3CO2)4 acetate heteronuclear complexes as precursors in the liquid-phase diphenylacetylene (DPA) hydrogenation have been studied. It has been established that the reaction over the Pd–Cu/Al2O3 catalyst proceeds more selectively than over the commercial Lindlar catalyst; in addition, high activity is achieved at a substantially lower palladium content. The maximum selectivity of DPA hydrogenation is observed with the catalyst reduced in a hydrogen atmosphere without any intermediate calcination that can result in the destruction of the bimetallic acetate complex. FTIR spectroscopy data for adsorbed CO show that the high selectivity of hydrogenation is due to the formation of homogeneous Pd–Cu particles and to the absence of monometallic palladium particles. This can be explained by the retention of the initial complex structure at all of the catalyst preparation stages until the formation of bimetallic particles during hydrogenation.

Unsupported NiMo catalysts prepared from a novel partly-sulfided complex precursor for dibenzothiophene hydrodesulfurization

A new partly-sulfided Ni–Mo dimetallic complex, [Ni(H2O)6][Mo2O2S2(edta)]·2H2O (edta = ethylenediaminetetraacetate) was synthesized. The complex was decomposed either in situ during the course of a dibenzothiophene (DBT) hydrodesulfrization (HDS) test or ex situ through sulfidation by H2S/N2 and two unsupported catalysts were obtained. These two catalysts and reference catalyst were characterized by XRD, BET and HRTEM. Textural and catalytic properties of these NiMo catalysts were strongly influenced by the nature of the precursor and the activation procedure. The introduction of edta ligand in the complex precursor resulted in the dispersion increase of nickel phases in these two catalysts. For these two catalysts, the ex situ activation method led to higher surface area, bigger pore volume, lower number of MoS2 layers and shorter MoS2 slabs than that led by the in situ activation method. The use of ex situ activation method led to a poor HDS activity and high hydrogenation selectivity while using in situ activation method, a net increase in HDS activity and initial rate constant was observed.

ChemInform Abstract: Catalytic Hydrogenation by Noble‐Metal Nanocrystals with Well‐Defined Facets: A Review

AbstractReview: 72 refs.

Partial hydrogenation of acetylene over a NiTi-layered double hydroxide supported PdAg catalyst

Supported PdAg/NiTi-LDH with rich defective sites was synthesized and exhibited high activity and selectivity in the partial hydrogenation of acetylene.

Bicontinuous zeolitic imidazolate framework ZIF-8@GO membrane with enhanced hydrogen selectivity.

Through layer-by-layer (LBL) deposition of a graphene oxide (GO) suspension on a semicontinuous ZIF-8 layer, we have developed a novel bicontinuous ZIF-8@GO membrane. Since only the gaps between the ZIF-8 crystals are sealed by the GO layer due to capillary forces and covalent bonds, the gas molecules can only permeate through the ZIF-8 micropore system (0.34 nm). Therefore, the ZIF-8@GO membranes show high hydrogen selectivity. At 250 °C and 1 bar, the mixture separation factors of H2/CO2, H2/N2, H2/CH4, and H2/C3H8 are 14.9, 90.5, 139.1, and 3816.6, with H2 permeances of about 1.3 × 10(-7) mol·m(-2)·s(-1)·Pa(-1), which is promising for hydrogen separation and purification by molecular sieving.

Does reduced or non-reduced biomass feed produce more gas in aqueous-phase reforming process?

There has been increasing interest in the production of gaseous and liquid biofuels from biomass. Biomass feed type and its content to be used in the conversion process are very important parameters to produce high yield biofuel. In this study, reduced and non-reduced forms of biomass-derived compound (glucose) and actual biomass hydrolysate feeds were evaluated to produce hydrogen-rich gas mixture by aqueous-phase reforming (APR) in presence of supported Ru catalyst. Various hydrogenation conditions were tested for effective conversion. The results showed that reduced solutions always produced significantly higher gas yield with high hydrogen selectivity. Although biomass hydrolysate was composed of variety of complex compounds, it exhibited significantly better performance compared to glucose, simple biomass model compound.

Preparation of magnetic mesoporous core–shell nanocomposites for cinnamic acid hydrogenation

A novel magnetic mesoporous core–shell nanocomposite Fe3O4@nSiO2@mSiO2@Ni–Co–B was prepared by the combination of a modified Stober sol–gel process, a surfactant-templating method and self-assembly. It has a multi-shell structure with ferroferric oxide as core, dense nonporous silica and mesoporous silica as middle layers in sequence and an Ni–Co–B amorphous alloy as outer layer, as confirmed by transmission electron microscopy and nitrogen adsorption–desorption. This nanocomposite showed high activity and good selectivity in the selective hydrogenation of cinnamic acid to hydrocinnamic acid. Notably, it can be easily separated by a magnet after reaction due to its high magnetism and recycled effectively five times.

Toward stable nickel catalysts for aqueous phase reforming of biomass-derived feedstock under reducing and alkaline conditions

Nickel nanoparticles supported on carbon nanofibers (CNF) can be stabilized in aqueous phase processes at elevated temperatures and pressures by tuning the reaction conditions to control Ni oxidation and leaching. As a showcase, Ni/CNF was used for the production of hydrogen via aqueous phase reforming of ethylene glycol (EG). Under standard conditions (T=230°C, inert atmosphere, 1wt.% EG), extensive catalyst deactivation occurred as a result of Ni particle growth. The extent of Ni particle growth was diminished either by using a more reducing environment by introducing additional H2 into the reactor or by increasing the concentration of reactant. Deactivation of the Ni/CNF catalyst due to particle growth was almost completely prevented by addition of KOH to the reaction mixture. Stable H2 production was achieved with high hydrogen selectivity (99%) during 50h on stream by addition of KOH, while without KOH the catalyst lost 93% of its initial activity and the H2 selectivity was lower (90%). The increased stability of Ni particles under both alkaline and reducing conditions is ascribed to the suppression of Ni leaching, which prevented subsequent particle growth via Ostwald ripening.

Catalytic reforming of glycerol in supercritical water with nickel-based catalysts

The catalytic performance of nickel catalysts supported on La2O3, α-Al2O3, γ-Al2O3, ZrO2, and YSZ for supercritical water reforming of glycerol was investigated. Experiments were conducted in a tubular reactor made of Inconel-625 with the temperature range of 723–848 K under a pressure of 25 MPa. Carbon formation causing operation failure was observed for α-Al2O3, γ-Al2O3 and ZrO2 at temperatures higher than 748, 798 and 823 K, respectively. Ni/La2O3 exhibited the highest H2 yield where almost complete conversion was obtained at 798 K. Moderate space velocities (WHSV = 6.45 h−1) and glycerol feed concentration (5wt.%) favor high hydrogen selectivity and yield. Methanation is favored at a low WHSV or high glycerol feed concentration, resulting in a lower H2 yield. Increasing Ni loading on the Ni/La2O3 catalyst strongly promoted the reforming, water–gas shift, and methanation reactions, which contributed significantly to the product species distribution.

Comparative study of propane steam reforming in vanadium based catalytic membrane reactor with nickel-based catalysts

The performance of catalytic membrane reactor with Pd-coated V membrane was examined for steam reforming of propane. The long term reforming experiment confirmed the stability of the V membrane with high hydrogen selectivity and permeability. The effect of types of hydrogen permeable membranes on the performance of the catalytic membrane reactor was studied by comparing Pd-coated V, Pd–23Ag, and Pd–10Ag membranes. The types of hydrogen separation membranes (i.e. hydrogen removal rates) did not have a marked effect on the propane conversion rates, while the product compositions were largely influenced by the hydrogen removal rate. Varying metal oxide supports of Ni-catalysts resulted in significant differences in the product compositions. Further, the evaluation of various catalyst-support systems (9wt%Ni–1wt%M/CeO2, M = Co, Pt, Ag, Ru) revealed that hydrogen yield was the highest when 1wt%Ag was added to Ni/CeO2. However, it was also found that excessive secondary metal additions can have negative impact on the catalytic behaviour of parent catalysts.

Mesoporous organic Pd-containing catalysts for the selective hydrogenation of conjugated hydrocarbons

Palladium catalysts supported on ordered organic mesoporous polymers were synthesized. The catalysts are characterized by the narrow size distribution of palladium nanoparticles with an average particle size of 2.2–5.2 nm. They demonstrate high catalytic activity and selectivity in phenylacetylene hydrogenation (896–2590 min−1, selectivity 89–98%). High activity and selectivity for alkenes are observed in the hydrogenation of conjugated dienes (for isoprene, TOF = 1850–5000 min−1, selectivity 99%; for 2,5-dimethyl-2,4-hexadiene, TOF = = 1294–2400 min−1, selectivity 100%; for 1,4-diphenyl-1,3-butadiene, TOF = 14–22 min−1, selectivity 7–16%). A dependence of the selectivity on the nature of the support and substrate was found for the hydrogenation of 1,4-diphenyl-1,3-butadiene.

Hydrogen production from ethanol decomposition by microwave plasma TIAGO torch

Abstract This paper describes the study of molecular hydrogen production from ethanol decomposition by argon microwave TIAGO discharge in air ambiance at atmospheric pressure. In order to estimate the influence of the experimental conditions on the hydrogen production, a wide range of Ar flows, input powers and ethanol flows were tested. The simultaneous use of emission spectroscopy and mass spectrometry techniques allowed us to gain knowledge about the mechanisms which lead to the obtaining of hydrogen and other by-products (C2H2, C(s) …) at the plasma exit. Results showed a great capability of TIAGO discharges to withstand ethanol introduction as well as an almost complete ethanol decomposition (higher than 99.6%) with high hydrogen selectivity; argon and ethanol flows were found to be the key parameters in the by-products formation.

Mechanistic insights into the effects of support on the reaction pathway for aqueous-phase hydrogenation of carboxylic acid over the supported Ru catalysts

Several supported Ru catalysts, Ru/TiO2, Ru/ZrO2, Ru/SiO2, Ru/γ-Al2O3 and Ru/SiO2-Al2O3, were prepared and investigated for propanoic acid aqueous-phase hydrogenation. H2-TPR, NH3-TPD, pyridine-FTIR and propanoic acid-DRIFTS techniques were performed to explore the metal–support interaction, acid sites and key adsorption species. The effect of support on the reaction pathway of CO hydrogenation and decarbonylation of acyl species was discussed. Compared with Ru/ZrO2 and Ru/SiO2 catalysts, high selectivity of CO hydrogenation was obtained over the catalysts with more Lewis acid sites, such as Ru/γ-Al2O3 and Ru/SiO2-Al2O3 catalysts. The DRIFTS results suggest that the formation of adsorption species (acyl, carboxylate and carboxylic acid) is strongly depended on the nature of support. The metal–acid bifunctional sites are indispensable for the CO hydrogenation of acyl. However, the decarbonylation of acyl on the metal sites requires the relatively weak metal–support interaction and few of Lewis acid sites.

The Pt‐Enriched PtNi Alloy Surface and its Excellent Catalytic Performance in Hydrolytic Hydrogenation of Cellulose

Ni-based catalysts are currently a subject of intense research in the hydrolytic hydrogenation of cellulose. We previously reported that Ni/ZSM-5 catalyst gave high yield of hexitols. However, Ni-based catalysts suffered fast deactivation in hot-compressed water. In this follow-up study we designed highly active Ni-based bimetallic catalysts with excellent hydrothermal stability for the hydrolytic hydrogenation of microcrystalline cellulose. PtNi/ZSM-5 shows a 76.9 % yield of hexitols, which is the best obtained so far in the hydrolytic hydrogenation of microcrystalline cellulose over Ni-based catalysts. Furthermore, the yield of hexitols remained greater than 55 % after the catalyst was reused for 4 times. The results showed that PtNi nanoparticles were formed with a Pt-enriched alloy surface as confirmed by XRD, H2-TPR (temperature-programmed H2 reduction), XPS (X-ray photoelectron spectroscopy), and H2-TPD (temperature-programmed H2 desorption). The surface features of these nano-particles were characterized by CO-TPD (temperature-programmed CO desorption), CO-FTIR (CO adsorption FTIR spectroscopy), HRTEM (high resolution TEM), and O2-TPO (temperature programmed oxidation) and this special surface structure may be responsible for the high activity, selectivity, and stability in the hydrolytic hydrogenation of cellulose in hot-compressed water.

Development of Pd Alloy Hydrogen Separation Membranes with Dense/Porous Hybrid Structure for High Hydrogen Perm-Selectivity

For the commercial applications of hydrogen separation membranes, both high hydrogen selectivity and permeability (i.e., perm-selectivity) are required. However, it has been difficult to fabricate thin, dense Pd alloy composite membranes on porous metal support that have a pore-free surface and an open structure at the interface between the Pd alloy films and the metal support in order to obtain the required properties simultaneously. In this study, we fabricated Pd alloy hydrogen separation membranes with dense/porous hybrid structure for high hydrogen perm-selectivity. The hydrogen selectivity of this membrane increased owing to the dense and pore-free microstructure of the membrane surface. The hydrogen permeation flux also was remarkably improved by the formation of an open microstructure with numerous open voids at the interface and by an effective reduction in the membrane thickness as a result of the porous structure formed within the Pd alloy films.

Ternary Ni–Al–Fe catalysts for ethanol steam reforming

Ternary mixed oxides prepared from takovite/reevesite Ni3Al1−xFex precursors were tested in ethanol steam reforming for hydrogen production. The influence of the trivalent cation (Al3+ or Fe3+) on phase composition and derived catalytic performance of the resulting oxides was studied. The physico-chemical properties of the hydrotalcite-like precursors and related oxides were characterized by ICP, XRD, TGA-DSC, Raman, H2-TPR, and TEM analyses. Compared to pure binary systems (Ni3Al and Ni3Fe), the ternary systems showed the best performance in ethanol reforming, leading to high and stable hydrogen selectivity of up to ca. 70% in 100 h reaction tests. The increase in activity can be attributed to a cooperative effect between aluminum and iron, favoring ethanol dehydrogenation as the primary step, followed by acetaldehyde reforming and/or cracking, reverse water gas shift, and methanation, and concomitantly limiting the dehydration route to ethylene.

Hydrogen production by steam reforming of biomass-derived glycerol over Ni-based catalysts

The steam reforming of bio-glycerol for the production of hydrogen has been investigated in a fixed-bed reactor containing spherical particle of Ni supported on γ-Al2O3 as catalyst. Several catalysts were prepared by the dry impregnation method at different calcination temperatures (750–950°C) with/without the addition of various alkaline promoters (K, Ca, Sr). The physical and chemical properties of the prepared catalysts were characterized by nitrogen (N2) physisorption, X-ray diffraction (XRD), temperature-programmed reduction, thermogravimetric analysis, scanning electron microscopy-energy dispersive X-ray spectroscopy and transmission electron microscopy techniques. The Ni/γ-Al2O3 catalysts showed a high glycerol conversion and hydrogen selectivity, however they gradually deactivated due to the formation of carbon over those catalysts.Nevertheless, it was found that the catalysts calcined at high temperatures could inhibit the formation of carbon without affecting the glycerol conversion and hydrogen selectivity. The addition of alkaline promoters caused a slight decrease in the glycerol conversion, but also reduced the formation of carbon and thereby increased the long-term stability of the catalyst.

Bio-Inspired Polydopamine: A Versatile and Powerful Platform for Covalent Synthesis of Molecular Sieve Membranes

Inspired by the bioadhesive ability of the marine mussel, a simple, versatile, and powerful synthesis strategy was developed to prepare highly reproducible and permselective molecular sieve membranes by using polydopamine as a novel covalent linker. Attributing to the formation of strong covalent and noncovalent bonds, ZIF-8 nutrients are attracted and bound to the support surface, thus promoting the ZIF-8 nucleation and the growth of uniform, well intergrown, and phase-pure ZIF-8 molecular sieve membranes. The developed ZIF-8 membranes show high hydrogen selectivity and thermal stability. At 150 °C and 1 bar, the mixture separation factors of H2/CO2, H2/N2, H2/CH4, and H2/C3H8 are 8.9, 16.2, 31.5 and 712.6, with H2 permeances higher than 1.8 × 10(-7) mol·m(-2)·s(-1)·Pa(-1), which is promising for hydrogen separation and purification.