H2 Chemisorption Research Articles

Stabilization of Pt in SiO2–Al2O3 Microspheres at High Mechanical Resistance, Promoted with W Oxides for the Combustion of CO

This study shows the development of a combustion promoter for the oil-refining process called fluid catalytic cracking (FCC). The investigation of a catalyst prepared for the combustion of CO composed of 0.05 wt% Pt supported on SiO2–Al2O3–0.5 wt% W microspheres with high mechanical resistance, promoted with tungsten oxides (WOx) that can inhibit the sintering of Pt, is reported. The addition of WOx in SiO2–Al2O3 inhibited the decrease in the specific area when calcined from 550 °C to 950 °C. SiO2–Al2O3 support in the form of calcined microspheres with average diameters between 70–105 µm were produced by spray drying, using two atomization discs with vanes of different geometry: a straight rectangular blade disc (DAR) and a curved rectangular vanes disc (DAC). The DAR disk produced whole microspheres, while the DAC had hollow and broken microspheres. The microspheres were characterized by XRD, SEM, optical microscopy, N2 physisorption (BET area) and fracture resistance tests. The Pt catalysts were evaluated by TPR, H2 chemisorption and CO combustion. The catalyst of 0.05 wt% Pt/SiO2–Al2O3–0.5 wt% turned out to be the most stable. A thermal stabilization effect was observed at contents lower than 1 wt% W that allowed it to inhibit the sintering of the Pt catalyst.

New findings regarding the role of copper entity particle size on the performance of Cu/ceria-based catalysts in the CO-PROX reaction

The preferential oxidation of CO in H2-rich mixtures has been studied using Ce0.8Zr0.2O2-supported Cu catalysts containing increasing amounts of copper [1 wt% (Cu1/CZ), 2 wt% (Cu2/CZ) and 4 wt% (Cu4/CZ)]. The oxide support was prepared by co-precipitation and the copper was incorporated using the wetness impregnation method. The catalysts were characterized using N2 adsorption, XRD, STEM-XEDS, H2-TPR, H2 chemisorption and XPS techniques. In particular, the complementarity of electron microscopy and hydrogen chemisorption techniques was found to be very useful for elucidating one of the most challenging properties of copper catalysts, namely their dispersion. The results show that the Cu1/CZ catalyst is the most active in the CO-PROX reaction at low temperatures (<125 °C), despite having a lower copper content. The results are discussed and correlated with the textural properties of the catalysts and with parameters such as metal dispersion and the binary interfacial active sites.

Highly stable platinum monolith catalyst for the hydrogenation of vegetable oil

In the present work, a novel structured platinum catalyst where the Pt is supported on an anodized aluminum monolith was studied for the hydrogenation of sunflower oil. The catalytic tests were carried out in a monolithic stirred semi-batch reactor at temperatures between 433 and 473 K, and hydrogen pressures from 2.7 to 5.4 atm. The monoliths were prepared using H2PtCl6 and Pt(C5H7O2)2 metal precursors and characterized by temperature programmed reduction, N2 adsorption isotherms, H2 chemisorption, scanning electronic microscopy, inductively coupled plasma-atomic emission spectroscopy, and ultrasound adherence tests. Response surface methodology was used to study the relationship between the process variables and C = C conversion, concentration of trans-isomers and selectivity toward monosaturated (S1) and saturated (S2) fatty acids.The catalysts showed to be active, reaching a conversion of 18% at 120 min. The H2PtCl6 impregnated monolith exhibited low selectivity towards trans-isomer formation, maintaining its initial catalyst activity after 40 consecutive uses, without modifications on S1 and S2. The results indicated that platinum monolith catalysts could be an affordable alternative to commercial Ni catalysts, removing the filtration and bleaching stages, hence reducing the processing costs.

Regulating the nanoscale intimacy of metal and acidic sites in Ru/γ-Al2O3 for the selective conversions of lignin-derived phenols to jet fuels

Catalytic hydrodeoxygenation (HDO) of biomass-derived oxy-compounds to advanced hydrocarbon fuels usually requires bifunctional catalysts containing metals and acidic sites. The appropriate tuning of metal and/or acidic active sites at interfaces of bifunctional catalysts can significantly improve catalyst activity and product selectivity. Here, 4-trifuoromethyl salicylic acid (TFMSA), as a hydrothermal stable organic acid, was employed to tailor the bifunctional interface of Ru/γ-Al2O3 to enhance the catalytic performance on converting lignin-derived phenols to jet fuel range cycloalkanes. More than 80% phenol was converted into cyclohexane at 230 °C for 1 h over Ru/γ-Al2O3 modified by TFMSA, which was about three times higher than that over unmodified Ru/γ-Al2O3. X-ray diffraction (XRD), Transmission electron microscope (TEM), H2 chemisorption, and energy dispersive X-ray spectroscopy (EDS) elemental mapping results indicated that Ru nanoparticles and TFMSA were well distributed on γ-Al2O3, and a nanoscale intimacy between Ru and TFMSA was reached. Meanwhile, Fourier transform infrared spectroscopy after pyridine adsorption (Py-FT-IR) analysis proved that Brønsted acidic sites on the catalytic interfaces of TFMSA modified Ru/γ-Al2O3 had been improved. Moreover, the kinetic and density functional theory (DFT) results suggested that the synergistic effects of adjacent Ru nanoparticles and acidic sites were crutial for promoting the rate-limiting conversion step of phenol HDO to cyclohexane.

Bimetallic metal organic framework-templated synthesis of a Cu-ZnO/Al2O3 catalyst with superior methanol selectivity for CO2 hydrogenation

It is highly desirable to develop inexpensive and highly selective catalyst for CO2 hydrogenation to methanol and Cu/ZnO/Al2O3 is a promising formulation. Herein, we report the design and synthesis of a Cu-ZnO/Al2O3 catalyst via a bimetallic metal organic framework (MOF)-templated strategy (termed Cu-ZnOMOF⊂Al2O3) and shed light on the role of the Cu-Zn@MOF precursor in this system for methanol synthesis. The developed Cu-ZnOMOF⊂Al2O3 exhibited high methanol selectivity (86.9%) and methanol space-time yield (407.2 gMeOH•kgcat−1•h−1) at higher CO2 conversion (9.1%) in comparison with the conventional Cu-ZnONO3/Al2O3 catalyst (79.6% and 209.0 gMeOH•kgcat−1•h−1, and 5.1%, respectively) at 240 ºC under 3.0 MPa. Spectroscopic characterization (TEM, XPS, EDX, in-situ DRIFTS) coupled with N2O chemisorption and temperature-programmed desorption of CO2 and H2 revealed that the surface of the new Cu-ZnOMOF⊂Al2O3 catalyst possesses higher Cu dispersion, surface-enriched ZnO and more Cu-ZnO interfacial sites, which leads to higher capability for CO2 and H2 adsorption and activation. These are considered to be the origin of higher methanol selectivity and enhanced activity of the catalyst prepared by the MOF-templated strategy for CO2 hydrogenation. This work offers a novel approach to optimizing Cu-ZnO/Al2O3 catalyst for CO2 hydrogenation to methanol.

Glycerol hydrogenolysis over Ru-Cu bimetallic catalysts supported on modified zirconias

Ruthenium-copper bimetallic catalysts supported on modified zirconia (m-ZrO2, 2%CaO-ZrO2, 3%SO4-ZrO2 and 10%WO3-ZrO2) were investigated in hydrogenolysis of glycerol in aqueous solution to produce 1,2-propanediol (1,2-PDO). Catalysts were characterized by N2 physisorption (BET), H2 and CO chemisorption, X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Active metallic phase consists of Ru-Cu nanoparticles with average diameter of 1.2 nm when supported on m-ZrO2 and 2%CaO-ZrO2, and larger particles on 3%SO4-ZrO2 and 10%WO3-ZrO2. In all cases, the addition of Cu to the Ru-based catalysts resulted in a decrease in glycerol conversion and increase in selectivity to 1,2-PDO. At 453 K, the best performing catalyst was bimetallic Ru-Cu/m-ZrO2. The catalysts supported on 3%SO4-ZrO2 showed activity well below expectations, likely due to sulfur poisoning. On the other hand, catalysts supported on 2%CaO-ZrO2 or 10%WO3-ZrO2 showed adequate activity. An increase in 40% in H2 pressure decreased 1,2-PDO selectivity but caused a ten-fold increase in TOF over Ru-Cu/10%WO3-ZrO2, to around 0.11 s−1. Cu addition to Ru lead to site blockage, with a beneficial effect on tuning selectivity towards C-O cleavage, and depressing C-C cleavage.

Observation of an Intermediate to H2 Binding in a Metal-Organic Framework.

Coordinatively unsaturated metal sites within certain zeolites and metal-organic frameworks can strongly adsorb a wide array of substrates. While many classical examples involve electron-poor metal cations that interact with adsorbates largely through physical interactions, unsaturated electron-rich metal centers housed within porous frameworks can often chemisorb guests amenable to redox activity or covalent bond formation. Despite the promise that materials bearing such sites hold in addressing myriad challenges in gas separations and storage, very few studies have directly interrogated mechanisms of chemisorption at open metal sites within porous frameworks. Here, we show that nondissociative chemisorption of H2 at the trigonal pyramidal Cu+ sites in the metal-organic framework CuI-MFU-4l occurs via the intermediacy of a metastable physisorbed precursor species. In situ powder neutron diffraction experiments enable crystallographic characterization of this intermediate, the first time that this has been accomplished for any material. Evidence for a precursor intermediate is also afforded from temperature-programmed desorption and density functional theory calculations. The activation barrier separating the precursor species from the chemisorbed state is shown to correlate with a change in the Cu+ coordination environment that enhances π-backbonding with H2. Ultimately, these findings demonstrate that adsorption at framework metal sites does not always follow a concerted pathway and underscore the importance of probing kinetics in the design of next-generation adsorbents.

Dynamics of Initial Hydrogen Spillover from a Single Atom Platinum Active Site to the Cu(111) Host Surface: The Impact of Substrate Electron-Hole Pairs.

The initial impulsive diffusion of hot hydrogen atoms resulted from the dissociative chemisorption of H2 at atomically dispersed Pt atoms embedded in Cu(111) is investigated using ab initio molecular dynamics. Upon dissociation, one of the two hydrogen atoms tends to roam away from the dissociation site while the other remains trapped. It is shown that the fraction of diffusion and the average diffusion length increase with the incident energy and H2 vibrational excitation, due apparently to the increased initial kinetic energy of the hot atoms. Most importantly, the strong interaction with surface electron-hole pairs, modeled using an electronic friction model, is shown to play an important role in rapid energy dissipation and significant retardation of the impulsive diffusion.

Effect of Sn content on Pt/CNT electrocatalysts for direct ethanol fuel cell application

AbstractSeveral bimetallic PtSn catalysts supported on multiwalled carbon nanotubes for ethanol electro‐oxidation were prepared by conventional impregnation‐reduction method. The Pt loading was kept at 20 wt.% and Pt:Sn atomic ratios of 5:1, 3:1, and 1:1 were selected. The catalysts were structurally characterized by temperature programmed reduction, X‐ray diffraction, X‐ray photoelectron spectroscopy, H2 chemisorption, cyclohexane dehydrogenation reaction, and transmission electron microscopy. The electrochemical characterization of the electrocatalytic materials was carried out in acid medium by cyclic voltammetry, linear sweep voltammetry, chronoamperometry, and CO stripping techniques. Among the different stoichiometries tested, the Pt(20)Sn(12.17)/CNT catalyst exhibited the highest electrocatalytic activity for ethanol oxidation reaction, with mass current density of 189.5 mA mgPt−1 at 796 mV (vs. Ag/AgCl).

Studies of New Iridium Catalysts Supported on Modified Silicalite-1-Their Structure and Hydrogenating Properties.

This paper investigates the catalytic properties of the iridium catalysts supported on modified silicalite-1. Post-synthesis modification of silicalite-1, with solutions of ammonium compounds (NH4F and NH4OH), appeared to be an efficient method to generate the acidic sites in starting support. The modification of support led not only to changes in its acidity but also its porosity—formation of additional micro- and mesopores. The novel materials were used as supports for iridium. The iridium catalysts (1 wt.% Ir) were characterized by N2 adsorption/desorption measurements, temperature-programmed reduction with hydrogen (TPR-H2), H2 chemisorption, transmission electron microscopy (TEM), temperature-programmed desorption of ammonia (TPD-NH3), X-ray photoelectron spectroscopy (XPS) and tested in the hydrogenation of toluene reaction. The catalytic activity of iridium supported on silicalite-1 treated with NH4OH (higher porosity of support, better dispersion of active phase) was much higher than that of Ir supported on unmodified and modified with NH4F silicalite-1.

Screening of mono and bimetallic catalysts for the dry reforming of methane

A series of nine different mono and bimetallic catalysts based on Ni, Rh and Pd supported on γ-Al2O3 or CeO2-Al2O3 was screened and compared in terms of activity and stability for the dry reforming of methane (DRM) reaction. All catalysts were prepared by the incipient wetness impregnation (IWI) method and characterized by XRD, XRF, TPR, H2 chemisorption and N2 physisorption. The used techniques aimed at determining crystalline phases, metal loading and dispersion and textural properties, which are properties that will affect the catalytic performance. The reactions were carried out in a fixed bed quartz reactor with temperatures ranging from 700° to 800 °C, WHSV 30 L gcat−1 h−1 and CH4:CO2 = 1 for periods of at least 48 h. All monometallic Ni based catalyst suffered from deactivation by coke deposition in the first hours of reaction at 700 °C. However, the original catalytic performance of these catalysts was restored after a regeneration treatment. At higher temperatures (800 °C), the 15%Ni/CeO2-Al2O3 catalyst presented no obvious signs of deactivation over the course of 48 h. Monometallic Pd/CeO2-Al2O3 catalysts, despite presenting higher turnover frequencies (TOF) when compared to monometallic and bimetallic Ni based catalysts, lost activity due to coke deposition. Both monometallic Rh based catalysts (0.5%Rh/CeO2-Al2O3 and 1%Rh/CeO2-Al2O3) presented a remarkable activity and stability with no signs of deactivation for 96 h TOS. The 0.5%Rh/CeO2-Al2O3 catalyst presented the highest TOF values among all screened catalyst with TOFCH4 of 9.9 s−1 and TOFCO2 of 12 s−1.

Tailoring the yttrium content in Ni-Ce-Y/SBA-15 mesoporous silicas for CO2 methanation

A series of nickel-cerium-promoted mesoporous silica (SBA-15) catalysts modified with different loadings of yttrium were synthesized by cetyltrimethylammonium bromide (CTAB)-assisted impregnation. The catalysts were tested in CO2 methanation reaction and characterized by N2 sorption, X-ray fluorescence (XRF), small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (XRD), H2 chemisorption, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), H2 temperature-programmed reduction (H2-TPR), CO2 temperature-programmed desorption (CO2-TPD), and thermogravimetric analysis coupled with mass spectrometry (TGA-MS). The best catalytic performance in CO2 methanation was found for Y-modified NiCe/SBA-15 catalysts compared to the unpromoted sample. The modification with 10 wt% of yttrium gave the highest CO2 conversion of 61% ± 2% at 350 °C. We attribute this increase to an improved dispersion of Ni, increased reducibility of Ni species, higher ratio of Ce3+/(Ce3+ + Ce4+), and increased moderate basicity found for 15Ni10Ce10Y/SBA-15. This paper shows that 10 wt% of Y loading not only improves the catalytic activity in CO2 methanation, but also gives stable performance. The tested 15Ni10Ce10Y/SBA-15 catalyst did not exhibit activity loss during 26 h of time-on-stream (TOS) experiment at 350 °C. Moreover, carbon deposits and sintered nickel particles could hardly be found in 15Ni10Ce10Y/SBA-15 catalyst used for 7 h.

The effect of support on RhFe/Al2O3 for ethanol synthesis via CO hydrogenation

Different alumina samples prepared with sol–gel, chemical precipitation and hydrothermal synthesis were used as supports of Fe-promoted Rh-based catalysts for ethanol synthesis via CO hydrogenation. The samples were characterized by means of N2-adsorpotion, XRD, H2-TPR, XPS, STEM, H2-TPD, DRIFTS, H2 and CO chemisorption. The results indicated that the Al2O3 prepared by hydrothermal synthesis exhibited nano-fiber morphology and constituted of mixed crystal phases, while Al2O3 prepared by sol–gel and chemical precipitation shows no changes of morphology and crystal phases compared with the commercial Al2O3. In addition, nano-fiber Al2O3-supported Rh-based catalyst shows higher ethanol selectivity, which is ascribed to the lower metal–support interaction, higher dispersion and stronger CO insertion ability.

Insights into the cyclic CO2 capture and catalytic methanation over highly performing Li-Ru/Al2O3 dual function materials

The combined CO2 capture and in-situ methanation using renewable hydrogen over dual function sorbent-catalyst materials is a chemical looping process with strong potential to increase the efficiency and reduce the cost of current CCU technologies. In this work, we set out to develop highly performing Lithium-Ruthenium/Al2O3 investigating synergic and mechanistic aspects involved in the alternate CO2 adsorption and hydrogenation phases. Catalysts with low Ru loading (max 1% wt.) and fixed dispersion on Al2O3 spheres were promoted with variable amounts of Li (1–5% wt.) and characterized by BET, PSD, XRD, H2 chemisorption, CO2-TPD, TG-MS, H2-TPSRx and CO2 catalytic methanation under continuous flow conditions. Transient CO2 storage/methanation cycles were studied in a fixed bed reactor that was operated at several temperature levels (250–350 °C) with alternate feed conditions of variable duration. The cycled CO2 adsorption and methanation were also investigated by in-situ DRIFT comparing results for xLi-Ru/Al2O3 materials against the reference Ru/Al2O3 catalyst. The favourable synergism existing at the nanoscale between the Li-aluminate sorbent phase and the catalytic Ru sites enhances the intrinsic activity of the DFMs that can guarantee high methane productivity and selectivity with low noble metal loadings.

Hydrogen production from methane autothermal reforming over CaTiO3, BaTiO3 and SrTiO3 supported nickel catalysts

Nickel supported on perovskite supports were investigated in the autothermal reforming of methane. The catalysts were prepared by incipient wetness impregnation and characterized by energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), N2 physisorption, H2 temperature programmed reduction (H2-TPR), H2 chemisorption, dehydrogenation of cyclohexane model reaction and Raman spectroscopy. The alumina supported catalyst exhibited highest initial conversion and selectivity to H2, however it deactivated. All catalysts with perovskite support were very stable, with Ni/CaTiO3 and Ni/BaTiO3 converting over 70% of the methane. Due to carbon formation, Ni/SrTiO3 conversion was only 50%. Turnover frequency was higher on perovskite supported catalysts. Deactivated Ni/Al2O3 favored total oxidation of methane instead of methane reforming, however the selectivity of catalysts supported on perovskites remained stable.

Interaction of hydrogen with palladium–copper nanoalloys

Doping porous carbons with palladium nanoparticles is known to enhance the hydrogen storage capacity of these materials. Alloying palladium with the non-expensive metal copper will reduce the cost of the nanoparticles. We have studied how alloying with copper affects the hydrogen adsorption properties of CumPdn clusters with m + n = 6. Formation of CumPdn nanoalloys is favorable, a fact consistent with the formation of bulk solid Cu–Pd alloys. Molecular adsorption of H2 and dissociative chemisorption are both exothermic, and dissociative chemisorption is energetically favorable compared to molecular adsorption. The geometric structures of the CumPdn clusters are maintained, in general, after molecular or dissociative adsorption of H2, with very few exceptions. Adsorption binding energies on some alloy nanoclusters rich in Cu are higher than adsorption binding energies on Pd6, so alloying with Cu may become a way to improve hydrogen adsorption in Pd-doped porous carbon materials.

Nitrided Ni/N-zeolites as efficient catalysts for the dry reforming of methane

N-ZSM-5 and N-beta zeolites with enhanced basic properties were prepared by substituting the framework oxygen with nitrogen using the high temperature nitridation with ammonia. The basic zeolites and their acidic counterparts were impregnated with Ni by the incipient wetness impregnation method and their catalytic properties for the dry reforming of methane (DRM) were investigated. The physicochemical properties of the prepared catalysts, such as the chemical state of nickel and properties of the framework nitrogen and acid-bases, were characterized by elemental analysis, 29Si MAS NMR, NH3 and CO2 TPD, IR, XPS, and H2 chemisorption. For all the catalysts, the DRM activity according to time on stream was compared by changing the temperature under the identical conditions. From the overall results, we demonstrated that the nitrided Ni/N-ZSM-5 exhibited superior DRM activity to the Ni/H-ZSM-5 especially at high temperature owing to the enhanced basic property and dispersion of Ni active species.

A Highly Selective and Stable Ruthenium‐Nickel Supported on Ceria Catalyst for Carbon Dioxide Methanation

AbstractThe performance of nickel, ruthenium, and nickel‐ruthenium impregnated on cerium oxide catalysts was tested in the methanation of carbon dioxide reaction. The nickel and ruthenium contents were 4 and 0.4 wt%, respectively. The properties of the catalysts were studied using elementary analysis, Brunauer‐Emmet‐Teller specific surface area measurements, X‐ray diffraction, temperature programmed reduction, temperature programmed desorption, H2 chemisorption and transmission electron microscopy. The results showed that the addition of ruthenium improves the catalytic performance by promoting the dispersion of nickel species over the surface of the cerium oxide support. The ruthenium‐nickel combination produced a stable catalyst that did not show any deactivation even after 75 hours on‐stream. At high feed gas total pressures (5 and 10 bar), the catalytic conversions of CO2 were close to the thermodynamic equilibrium values with a 100 % selectivity towards CH4 formation.

The effect of La2O3 and CeO2 modifiers on properties of Ni–Al catalysts for LNG prereforming

Ni/La–Al2O3 and Ni/Ce–Al2O3 catalysts with a small amount of promoters intended for prereforming of LNG were characterized by XRF, N2 adsorption-desorption, XRD, H2 chemisorption, HRTEM and XPS. The catalytic activity was evaluated in methane steam reforming both in the kinetic and diffusion regime, at temperatures characteristic of pre-reforming. Carbonaceous deposit was analysed by TPO-MS method. The nature and location of the coke were studied by HRTEM.La or Ce addition into Ni–Al system causes the increase of the active surface area of Ni by enhancing its dispersion. Studies at kinetic regime have shown that the promoted catalysts have almost twice the activity than reference Ni–Al catalyst. This effect was not confirmed by measurements in the diffusion regime on whole catalyst tablets. Almost identical textural properties of catalysts and diffusive limitations related to them but not the catalytic properties of the material itself appeared to be crucial factors. The presence of La (but not Ce) causes a significant increase in resistance to coking.

Catalytic reforming of tar model compound over La1-xSrx-Co0.5Ti0.5O3-δ dual perovskite catalysts: Resistance to sulfide and chloride compounds

Sr-containing La1.0-Co0.5Ti0.5O3 as dual perovskite materials were investigated for the steam reforming of the toluene (SRT) reaction. The impact of Sr-doping on tolerance towards tar contaminants (chloride & H2S) for the SRT reaction was also studied. Overall, an optimum catalyst composition of La0.8Sr0.2-Co0.5Ti0.5O3 gave superior reforming activity than others. At 700 °C (S/C = 2), La0.8Sr0.2-Co0.5Ti0.5O3 exhibited ∼ 90 % of toluene conversion and stable for 21 h. La0.8Sr0.2-Co0.5Ti0.5O3 also displayed 80 % and 65 % of toluene conversion in the presence of 0.1 % and 1% of trichloroethylene (TCE) at 700 °C. XRD analysis revealed the formation of dual perovskite structures for calcined Sr doped La1.0-Co0.5Ti0.5O3 materials and negligible Co agglomeration during SRT reaction. TGA analysis revealed that the formation of carbon was insignificant during the SRT reaction at 700 °C. Finally, the superior catalytic performance of La0.8Sr0.2-Co0.5Ti0.5O3 catalyst over others is attributed to the availability of surface Co species (H2 chemisorption), mobile O2 species, and an optimum basic character.