Temperature-programmed Reduction Research Articles

Optimization of Ni/ZnZr catalyst for enhanced syngas yield in catalytic pyrolysis of rice straw

To enhance the catalytic performance of nickel-based catalysts and improve their efficiency in biomass pyrolysis, a nickel-based catalyst supported on a ZnZr composite carrier was synthesized using the sol-gel method. The morphological changes of the catalyst before and after the reaction were observed using X-ray diffraction, scanning electron microscopy, nitrogen gas adsorption, temperature-programmed reduction, and other methods to analyze its catalytic performance. A series of experiments were conducted to explore the optimal conditions for the catalyst’s gas production, including carrier material ratios, loading amounts, residence time, and reaction temperature. The bimetallic carrier of Zn and Zr provided a higher specific surface area, allowing the metallic nickel to enter its mesopores. The synergistic effect of the bimetallic system facilitated the catalytic activity of nickel, significantly enhancing gas production. The maximum CO and H2 production were achieved at Zn/Zr = 6/4. The catalyst achieved an optimal gas yield of 507 mL/g at a residence time of 20 min and a reaction temperature of 800 °C, demonstrating strong stability.

Stable and selective conversion of ethylene to propylene and butylene using Ni-loaded dealuminated Beta zeolite catalyst

The selective conversion of ethylene into propylene (ETP) has garnered significant attention due to the growing demand for the product of this reaction in the petrochemical industry. In this study, we developed a series of Ni-loaded dealuminated Beta zeolite catalysts for the ETP reaction. The catalyst loaded with 0.07 wt% Ni showed stable and high catalytic activity with 28% propylene yield and 16% butylene yield, despite very low Ni content compared to previously reported catalysts. Temperature-programmed H2 reduction and NH3-desorption analyses showed that the active sites were Ni species grafted onto the defective silanols of dealuminated zeolites.

Exsolution-enhanced reverse water-gas shift chemical looping activity of Sr2FeMo0.6Ni0.4O6-δ double perovskite

This study investigates the structural evolution and redox characteristics of the double perovskite Sr2FeMo0.6Ni0.4O6-δ (SFMN) during hydrogen (H2) and carbon dioxide (CO2) redox cycles and explores the material performance in the Reverse Water-Gas Shift Chemical Looping (RWGS-CL) reaction. In-situ and ex-situ X-Ray Diffraction (XRD) and High-Resolution Transmission Electron Microscopy (HRTEM) studies reveal that H2 reduction at temperatures above 800 °C leads to the exsolution of bimetallic Ni-Fe alloy particles and the formation of a Ruddlesden-Popper (RP) phase. A core–shell structure with Ni-Fe core and a perovskite oxide shell is formed with subsequent redox cycles, and the resulting material exhibits better performance and high stability in the RWGS-CL process. Thermogravimetric (TGA) and Temperature Programmed Reduction (TPR) and Oxidation (TPO) analyses show that the optimal reduction and oxidation temperatures for maximizing the CO yield are around 850 °C and 750 °C respectively, and that the cycled material is able to work steadily under isothermal conditions at 850 °C.

Influence of CaCe ratio on the hydrogen production from ammonia over CaO-CeO2 supported Co catalysts

Hydrogen (H2) fuel has the potential to replace fossil fuel for generating electricity, clean energy and generating power. Ammonia (NH3) has the potential to overcome the challenges associated with storage, transportation, and use of hydrogen fuel. The catalytic decomposition of ammonia into hydrogen is studied over cobalt catalysts supported on CaO-CeO2 mixed oxide. The influence of the Ca/Ce ratio in the support composition on catalytic activity was investigated. The CaO-CeO2 mixed oxide support materials prepared with different Ca/Ce ratios (1:1, 2:1 and 3:1). The overall basicity of catalyst varied with the increase of Ca to CaO-CeO2 mixed oxide and showed maximum at Ca/Ce = 2. The cobalt catalysts are prepared with a nominal 5 wt% Co over CaO-CeO2 mixed oxide support with various Ca/Ce ratios. Among all prepared catalysts 5CoCaCe-21 (5 wt%Co on CaO-CeO2 mixed oxide with Ca/Ce = 2) showed highest activity. Surface area, X-ray diffraction (XRD), Temperature Program Reduction (TPR), Scanning Electron Microscopy (SEM), and CO2 Temperature Program Desorption (TPD) methods were used to characterize the synthesized materials. The high performance of 5CoCaCe-21 catalyst is due to high basicity, suitable metal support interactions, high surface area and easy reducibility of Co species resulting from its support favorable properties. The effect of cobalt loadings also studied on CaCe-21 support. The 10 wt%Co on CaCe-21 (10CoCaCe-21) showed highest activity among all other cobalt loadings. The 10CoCaCe-21 catalyst showed excellent stability for H2 production from NH3 during 70 h of time on study with different GHSVs.

In Situ Transmission Electron Microscopy to Study the Location and Distribution Effect of Pt on the Reduction of Co3 O4 -SiO2.

The addition of Pt generally promotes the reduction of Co3 O4 in supported catalysts, which further improves their activity and selectivity. However, due to the limited spatial resolution, how Pt and its location and distribution affect the reduction of Co3 O4 remains unclear. Using ex situ and in situ ambient pressure scanning transmission electron microscopy, combined with temperature-programmed reduction, the reduction of silica-supported Co3 O4 without Pt and with different location and distribution of Pt is studied. Shrinkage of Co3 O4 nanoparticles is directly observed during their reduction, and Pt greatly lowers the reduction temperature. For the first time, the initial reduction of Co3 O4 with and without Pt is studied at the nanoscale. The initial reduction of Co3 O4 changes from surface to interface between Co3 O4 and SiO2 . Small Pt nanoparticles located at the interface between Co3 O4 and SiO2 promote the reduction of Co3 O4 by the detachment of Co3 O4 /CoO from SiO2 . After reduction, the Pt and part of the Co form an alloy with Pt well dispersed. This study for the first time unravels the effects of Pt location and distribution on the reduction of Co3 O4 nanoparticles, and helps to design cobalt-based catalysts with efficient use of Pt as a reduction promoter.

Application fischer-tropsch synthesis: a review

This work was to evaluate the catalytic properties Ru/Cobalt/SBA-15 catalyst for Fischer-Tropsch synthesis (FTS). The molecular sieve SBA-15 synthesized by hydrothermal method with rice husk ashes (RHA) and with tetraethyl orthosilicate (TEOS). The Ru promoted Co/SBA-15 catalyst was prepared by wet impregnation method and was characterized by X-ray diffraction, X-ray energy dispersion spectrophotometer, N2 adsorption-desorption, temperature-programmed reduction and transmission electron microscopy. The Fischer-Tropsch synthesis using the catalysts were carried out to evaluate the catalysts activities and its effect on FTS product distribution. The synthesis was carried out in a slurry reactor operating at 513 K, 20 atm, CO : H2 molar ratio of 1 : 2. X-ray diffraction showed that the calcined cobalt catalyst did not modify the structure of SBA-15, proving that Co was present under the form of Co3O4 in the catalyst. The addition of cobalt in SBA-15 decreased the specific superficial area of the molecular sieve. By RTP results was found the ranges of temperature reduction typical of iron oxides phases. Fischer-Tropsch synthesis activity and C5+hydrocarbon selectivity increased with the addition of Ru. The increases in activity and selectivity were attributed to the increased number of active sites resulting from higher reducibility and the synergetic effect of Ru and Co. The most interesting fact to be pointed out is that the use of this catalytic system for the catalyst prepared with alternative source of silica and cheap (rice hull ash) showed high selectivity in liquid products, that is, in hydrocarbons with C5+ (88.2% w/w), higher than the catalyst prepared with conventional silica source.

Characterization and Testing of Exsolution-Based Solid Oxide Cells for Reversible Operations in CO2 Electrolysis

Reversible solid oxide cells (rSOCs) are a promising electrochemical technology able to work both as energy storage devices in solid oxide electrolysis (SOEC) mode, and as power generators in solid oxide fuel cell (SOFC) mode. rSOCs implemented for CO2 electroreduction into valuable CO-rich steams through electrolysis would provide opportunities for CO2 utilization, and hence become useful tools for the reduction of greenhouse gases emissions. High-temperature co-electrolysis of CO2/H2O mixtures has recently become of interest since high conversion and energy efficiency are thermodynamically favored in addition to the reduction in cell area-specific resistance when compared to pure CO2 electrolysis [1]. However, reversible operation with CO2-containing feeds requires developing flexible, high-performing, and long-lasting materials for the rSOCsManaging issues such as coking and low redox tolerance in the state-of-the-art (SoA) Ni-Yttria-stabilized-zirconia (Ni-YSZ) cermet fuel electrode in the rSOCs is crucial. Ni-YSZ cermet exhibits high electronic conductivity and electrochemical activity in hydrogen. Nonetheless, Ni is prone to oxidation due to operation under high steam concentrations, and rapid variations in the fuel supply. Additionally, Ni is well-known for its coke-formation tendency which becomes detrimental in CO2-rich mixtures for electrolysis [2]. Thus, ceramics with mixed ionic and electronic conductivity (MIEC) have emerged as alternative fuel electrodes thanks to the larger electrochemically active area compared to standard cermets. Among the MIEC electrodes, the SrTi0.3Fe0.7O3 (STF) perovskite has proven to give low polarization resistances especially when modification techniques such as exsolution of metal nanoparticles are employed [3]. This work focuses on the investigation of the electrocatalytic properties of exsolution-based STF electrodes operating with CO/CO2 and H2O/CO2 mixtures. The mixtures used were 50% CO2/50% CO, 25% H2O/25% CO2/25%H2/25%CO, and 45% H2O/45% CO2/10% H2. A comparison between the performance and microstructure of the studied electrode formulation is provided.Electrolyte-supported cells were manufactured via screen-printing of the electrode inks on scandia-stabilized zirconia (ScSZ) electrolytes. STF perovskite-based electrodes were used, namely: SrTi0.3Fe0.7O3 (STF), Sr0.95(Ti0.3Fe0.63Ni0.07)O3 (STF-Ni), and Sr0.95(Ti0.3Fe0.63Ru0.07)O3 (STF-Ru). The latter two formulations allowed the enhancement of the perovskite structure via exsolution of catalytic nanoparticles (Ni, Co alloyed with Fe) on the oxide surface during cell operation. Each cell configuration included a gadolinium-doped ceria (GDC) buffer layer coupled with an LSCF-GDC (La0.6Sr0.4Co0.2Fe0.8O3/Ce0.9Gd0.1O1.95) oxygen electrode. Baseline performances of cell mounting the Ni-YSZ cermet electrode were also evaluated for comparison with the perovskite alternatives, both in the short and long term. Electrochemical characterization was done via impedance spectroscopy, polarization experiments, and durability tests in potentiostatic mode. Chemical characterization was performed via X-ray diffraction, scanning electron microscopy, and temperature-programmed reduction analyses.Compared to Ni-YSZ, significant improvement in terms of reversibility and maximum current densities of the current-voltage (I/V) curves in both SOFC and SOEC modes is found on the STF-based cells at 750°C under CO/CO2 mixtures (Figure 1B). The initial difference in the performance of the STF cells with respect to the Ni-YSZ cermet in humidified H2 (SOFC mode, Figure 1A) was overcome by using the exsolved electrode formulations. Aging experiments up to 100 h performed in alternating operation modes from SOFC (6 h) to SOEC (6 h) indicated an initial performance degradation within the first 24 h for both the cermet and perovskite-based fuel electrodes which later stabilized in time. Compared to the undoped STF formulation, improvement in performance stability was observed for the exsolved STF-Ni and STF-Ru fuel electrodes while working under the target CO/CO2 mixture. This was attributed to the combination of the STF structure benefits (low polarization resistance towards CO/CO2 and H2O/CO2 mixtures) with the boost that metallic nanoparticles provide to the electrode’s heterogeneous catalytic reactivity and overall stability over time.

Pt-Doped Lanthanum Ferrites as Versatile Electrode Material for Solid Oxide Cells

La0.6Sr0.4Fe0.8Co0.2O3-δ (LSCF) alone or mixed with doped ceria represents the reference air electrode material for IT-SOFC/SOEC, thanks to its intrinsic MIEC nature and unrivaled catalytic activity towards oxygen exchange reactions. Nevertheless, a steep growth in cobalt demand for automotive (EVs) and storage applications is expected in the next decades, and ethical issues related to cobalt mining in politically unstable countries endanger cobalt supply chain [1]. Noble metal doping to a low extent ( ≤ 5% mol) has drawn attention as a valid strategy to provide the parent oxide structure with high catalytic activity [2][3]. Such amounts of platinum-group-metals (PGM) could be profitably harvested from secondary sources, such as spent automotive three-way catalysts (TWCs) [4], rendering their supply less dependent from localized low-grade ores. In particular, due to the tendency of PGM to be easily reduced to the metallic state, PGM-doped perovskites have found application mainly as fuel electrode materials. Noble metal exsolution endows the parent perovskite with finely dispersed nanoparticles firmly anchored to the oxide substrate, that display high catalytic activity and stability [5].Here, platinum-doping on strontium-substituted lanthanum ferrites is explored as an innovative strategy to enhance the parent perovskite catalytic activity both in reducing and oxidizing environment. The ultimate goal is the design of a multi-functional electrode for Reversible Solid Oxide Cells (r-SOCs). La0.6Sr0.4Fe1-xPtxO3-δ, X = 0.005, 0.01, 0.05 (LSFPtX) stoichiometries were successfully synthesized and characterized by means of X-ray Powder Diffraction (XPRD) (Fig. 1), thermogravimetric analysis (TG), oxygen temperature-programmed desorption (O2-TPD) and X-ray photoelectron spectroscopy (XPS). LSFPtX were tested in symmetric cells to evaluate their activity as air electrode materials in terms of polarization resistance vs. temperature and vs. pO2. The rate-limiting steps of oxygen exchange reactions were investigated by means of electrochemical impedance spectroscopy (EIS) fitting experimental data with equivalent circuit (EC) modelling and distribution of relaxation times (DRT). Results were compared both to the undoped (LSF) and to a commercially available state-of-art 20 mol% Co-substituted LSCF. LSFPtX structural evolution is evaluated at different pO2 and in several SOCs operational environments (5%H2/Ar, 100% CO2 and 50% CO2 : 50% CO). B-site exsolution was studied by means of temperature-programmed reduction (H2-TPR) and scanning electron microscopy (FE-SEM) to assess their applicability as fuel electrode materials as well. Finally, LSGM-based symmetric cells were tested as SOFC and CO2-SOEC, evaluating the operational reversibility and the long-term stability.[1] IEA, Total Cobalt Demand by Sector and Scenario, October 2022, pp. 2020–2040.[2] Marcucci, A., Zurlo, F., Sora, I. N., Placidi, E., Casciardi, S., Licoccia, S., & Di Bartolomeo, E. (2019). A redox stable Pd-doped perovskite for SOFC applications. Journal of Materials Chemistry A, 7(10), 5344-5352.[3] Marasi, M., Duranti, L., Luisetto, I., Fabbri, E., Licoccia, S., & Di Bartolomeo, E. (2023). Ru-doped lanthanum ferrite as a stable and versatile electrode for reversible symmetric solid oxide cells (r-SSOCs). Journal of Power Sources, 555, 232399.[4] Karim, S., & Ting, Y. P. (2021). Recycling pathways for platinum group metals from spent automotive catalyst: A review on conventional approaches and bio-processes. Resources, Conservation and Recycling, 170, 105588.[5] Kothari, M., Jeon, Y., Miller, D. N., Pascui, A. E., Kilmartin, J., Wails, D., ... & Irvine, J. T. (2021). Platinum incorporation into titanate perovskites to deliver emergent active and stable platinum nanoparticles. Nature Chemistry, 13(7), 677-682. Figure 1

Highlights on the key roles of interfaces between CeO2-based oxide and perovskite (LaMnO3/LaFeO3) in creating active oxygen species for soot oxidation

Design efficient catalyst which can activate oxygen molecules or supply active oxygen species is a key challenge for soot abatement under the much lower concentration of oxygen from gasoline vehicle exhaust. Herein, combining with the advantages of both CeO2-based oxide (CeO2–ZrO2–Y2O3–La2O3, CZ for short) and perovskite (LaMnO3 and LaFeO3) in oxygen storage/release, two hybrids catalysts, CZ-LaMnO3 (LM) and CZ-LaFeO3 (LF), with more oxygen vacancies and enhanced lattice oxygen transport at lower temperatures due to the heterointerface effects have been successfully synthesized for soot oxidation. Combining with X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), oxygen temperature-programmed desorption (O2-TPD) and H2temperature-programmed reduction (H2-TPR), it was found that electrons transfer from Ce3+ to Fe3+ and an interfacial La diffusion from LM to CZ may have been occurred in LF-CZ and LM-CZ, respectively, which leads to the increased unsaturated sites and oxygen vacancies. More importantly, the obvious enhancement of active surface lattice oxygen transport at low temperatures due to interfacial interaction has also been demonstrated in LM-CZ, which highly promotes the soot oxidation. And consequently, 5LM-CZ (with 5 wt% content of LM) showed the highest soot conversion activity, whose T50 (50 % soot conversion temperature) (379 °C) was lower than 5LF-CZ (395 °C) and CZ (401°C) at tight contact mode in 1 %O2/N2 atmosphere, indicating that the activation of lattice oxygen at the interface plays an important role in soot oxidation. Furthermore, when further varying the content of LM in xLM-CZ (x = 5 wt%, 10 wt%, 15 wt%, 20 wt%), it was found that 10LM-CZ, whose content of LM reached the monolayer dispersion capacity of CZ, exhibited the most abundant active surface lattice oxygen species due to the optimized interface area. As a result, 10LM-CZ displayed superior activity even than pure LM in both loose and tight contact with/without NO, indicating that the composite catalyst has a wide application environment. This work has a certain guiding significance for the utilization of heterointerface effect among different components to prepare effective soot oxidation catalyst with multi-components.

Palladium-Rhenium Catalysts for Selective Hydrogenation of Furfural: Influence of Catalyst Preparation on Structure and Performance

PdRe/Al2O3 catalysts are highly selective for hydrogenation of furfural to furfuryl alcohol (FAL). Moreover, the synergy between the metals can result in greater specific activity (higher turnover frequency, TOF) than exhibited by either metal alone. Bimetallic catalyst structure depends strongly on the metal precursors employed and their addition sequence to the support. In this work, PdRe/Al2O3 catalysts were prepared by: (i) co-impregnation (CI) and sequential impregnation (SI) of γ-Al2O3 using HReO4 and Pd(NO3)2, (ii) SI using NH4ReO4 and [Pd(NH3)4(NO3)2], (iii) HReO4 addition to a reduced and passivated Pd/Al2O3 catalyst, and (iv) impregnation with the double complex salt (DCS), [Pd(NH3)4(ReO4)2]. Raman spectroscopy and temperature-programmed reduction (TPR) evidence larger supported PdO crystallites in catalysts prepared using Pd(NO3)2 than [Pd(NH3)4(NO3)2]. Surface [ReO4]− species detected by Raman exhibit TPR peak temperatures from ranging 85 to 260 °C (versus 375 °C for Re/Al2O3). After H2 reduction at 400 °C, the catalysts were characterized by chemisorption, temperature-programmed hydride decomposition (TPHD), CO diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and scanning transmission electron microscopy (STEM) with energy-dispersive x-ray (EDX) spectroscopy. The CI catalyst containing supported Pd–Re alloy crystallites had a TOF similar to Pd/Al2O3 but higher (61%) FAL selectivity. In contrast, catalysts prepared by methods (ii–iv) containing supported Pd-Re nanoparticles exhibit higher TOFs and up to 78% FAL selectivity.

Preparation of SBA-15 supported Ru nanocatalysts by electrostatic adsorption-ultrasonic in situ reduction method and its catalytic performance for hydrogen storage of N-ethylcarbazole.

N-ethylcarbazole (NEC) is an ideal liquid organic hydrogen storage carrier. The development of efficient hydrogen storage catalysts can promote the large-scale application of this process. In this paper, SBA-15 supported Ru nanocatalysts (Ru/S15-SU) were synthesized by strong electrostatic adsorption (SEA)-ultrasonic in situ reduction method (UR). Ru/S15-SU was characterized by N2 adsorption-desorption, TEM, H2 temperature program reduction, FT-IR, XRD, and XPS analysis measures. The results showed that ultrafine Ru NPs were evenly distributed on the surface of SBA-15, and ultrasonic in situ reduction not only reduced Ru3+ to Ru0, but also produced a coordination effect between Ru and O, enhancing the interaction between Ru NPs and the carrier. Ru/S15-SU exhibited excellent catalytic performance in the hydrogenation reaction of NEC, and the hydrogen storage efficiency reached 99.31% at 130°C and 6 MPa H2 pressure, which is superior to that of commercial 5wt%Ru/Al2O3. The excellent catalytic hydrogenation performance can be attributed to the selective anchoring of ruthenium ions on the surface of SBA-15 via electrostatic adsorption, preventing the aggregation of Ru NPs and enhancing the interaction between SBA-15 and Ru NPs by ultrasonic in situ reduction. Ru/S15-SU had a lower NEC hydrogenation apparent activated energy (Ea) of 68.45 kJ/mol than 5wt%Ru/Al2O3 catalyst. This method provides a new approach for the green preparation of nanocatalysts without using any chemical reducing agents.

Investigation of the synergistic effect of O2/H2O pretreatment and Na addition on the NO-semichar reaction

The surface physicochemical features of semichar play a crucial role in determining its reactivity, dominating the subsequent reaction between semichar and NO. Therefore, the synergistic effect of O2/H2O pretreatment and Na addition on the microstructural characteristics of semichar and NO reduction characteristics is revealed through experimental and density functional theory (DFT) methods. Experimental results indicate that O2/H2O pretreatments with Na addition promote the development of pores. Micropores are considered the major pore structures in semichar. Based on Raman and laser-induced breakdown spectroscopy (LIBS) results, the combined effect of O2/H2O pretreatments and Na promotes the formation of small aromatic rings, exhibiting a positive correlation with molecular emissions. Temperature-programmed reduction experiments (TPR) demonstrate that the inclusion of Na in O2/H2O pretreatments enhances the reduction ability of NO. The reduction mechanism of NO-semichar is determined using the DFT method. The simulation results indicate that the adsorption of H2O during O2/H2O pretreatment is chemisorption and independent of Na atom. The additional Na reduces the energy gap of the NO-semichar, facilitating the decomposition of N2 by weakening the conjugated components of the aromatic structures.

Thermokinetic Study of Catalytic Pyrolysis of Medium-Density Fiberboards over Beta-Zeolite-Supported Platinum

Catalytic pyrolysis is an attractive alternative for converting biomass into energy and chemicals, replacing fossil sources. Efficient catalysts can be used to remove compounds containing oxygen during pyrolysis, improving the bio-oil properties and thus being an important route towards sustainability. Catalytic pyrolysis of medium-density fiberboard (MDF) residues over platinum (1%) supported on beta zeolite was carried out using a biomass/catalyst ratio of 1.0/0.2. The catalysts were characterized via Fourier transform infrared spectroscopy, flame atomic absorption spectrometry, X-ray diffraction, nuclear magnetic resonance, temperature-programmed reduction, and temperature-programmed desorption of ammonia. The thermokinetic and thermodynamic parameters were determined using the isoconversional and non-isothermal methods of Friedman, Flynn-Wall-Ozawa (FWO), and Kissinger-Ahakira-Sunose (KAS). The Friedman method was the most adequate to describe the reaction and thermodynamic parameters. The results show that the catalysts promote the reduction in activation energy compared to non-catalytic pyrolysis. Non-impregnated and impregnated catalysts showed different activation energies and thus different reactions. The addition of platinum slightly increased the activation energy due to the promotion of reactions that require more energy, for example, cracking and coke deposition.

How Pt Influences H2 Reactions on High Surface-Area Pt/CeO2 Powder Catalyst Surfaces.

The addition of platinum-group metals (PGMs, e.g., Pt) to CeO2 is used in heterogeneous catalysis to promote the rate of redox surface reactions. Well-defined model system studies have shown that PGMs facilitate H2 dissociation, H-spillover onto CeO2 surfaces, and CeO2 surface reduction. However, it remains unclear how the heterogeneous structures and interfaces that exist on powder catalysts influence the mechanistic picture of PGM-promoted H2 reactions on CeO2 surfaces developed from model system studies. Here, controlled catalyst synthesis, temperature-programmed reduction (TPR), in situ infrared spectroscopy (IR), and in situ electron energy loss spectroscopy (EELS) were used to interrogate the mechanisms of how Pt nanoclusters and single atoms influence H2 reactions on high-surface area Pt/CeO2 powder catalysts. TPR showed that Pt promotes H2 consumption rates on Pt/CeO2 even when Pt exists on a small fraction of CeO2 particles, suggesting that H-spillover proceeds far from Pt-CeO2 interfaces and across CeO2-CeO2 particle interfaces. IR and EELS measurements provided evidence that Pt changes the mechanism of H2 activation and the rate limiting step for Ce3+, oxygen vacancy, and water formation as compared to pure CeO2. As a result, higher-saturation surface hydroxyl coverages can be achieved on Pt/CeO2 compared to pure CeO2. Further, Ce3+ formed by spillover-H from Pt is heterogeneously distributed and localized at and around interparticle CeO2-CeO2 boundaries, while activated H2 on pure CeO2 results in homogeneously distributed Ce3+. Ce3+ localization at and around CeO2-CeO2 boundaries for Pt/CeO2 is accompanied by surface reconstruction that enables faster rates of H2 consumption. This study reconciles the materials gap between model structures and powder catalysts for H2 reactions with Pt/CeO2 and highlights how the spatial heterogeneity of powder catalysts dictates the influence of Pt on H2 reactions at CeO2 surfaces.

Nanostructured Ru(2 wt%)/PrxCe1−xO2-δ (x = 0, 0.12 and 0.25) materials for hydrodeoxygenation of guaiacol: Influence of oxygen vacancies on reactivity

To assess the influence of catalyst morphology and dopant on catalytic activity for the hydrodeoxygenation (HDO) of guaiacol, four Ru catalysts—Ru(2 wt%)/CeO2 irregular nanoparticles (Ru-1), Ru(2 wt%)/CeO2 nanocubes (Ru-2), Ru(2 wt%)/Ce0.88Pr0.12O2-δ nanocubes (Ru-3) and Ru(2 wt%)/Ce0.75Pr0.25O2-δ nanocubes (Ru-4) were prepared and characterized using transmission electron microscopy, X-ray diffraction analysis, Raman spectroscopy, hydrogen temperature-programmed reduction, X-ray photoelectron spectroscopy, and volumetric oxygen titration. The shape-dependent catalytic activities for the HDO of guaiacol over Ru-1 and Ru-2 were initially determined, presenting that Ru-2 exhibited higher activity than Ru-1. In addition, the effect of Pr doping into CeO2 on the desired activity was examined using Ru-2, Ru-3 and Ru-4, demonstrating that there is an optimal Pr content that maximizes the activity. The results obtained by the analytical methods with additional oxygen vacancy titration indicate that the activities of the catalysts are strongly correlated with the normalized oxygen vacancy densities.

In situ topologically prepared Co–Zn-based mixed metal oxide bimetallic catalysts for guaiacol hydrodeoxygenation

Bio-oil, derived from biomass pyrolysis, can be used as an alternative to fossil fuels after treatment through hydrodeoxygenation (HDO) reactions. In this study, a series of Co–Zn-based mixed metal oxide (Co-Zn-MMO) catalysts were synthesized using Co–Zn-based layered double hydroxide (Co-Zn-LDH) as a precursor. The catalysts were then used in the HDO reaction of guaiacol and larch wood-derived bio-oil. The Co–Zn-MMO catalysts were characterized via scanning electron microscopy, X-ray diffraction, Brunauer–Emmett–Teller analysis, X-ray photoelectron spectroscopy, hydrogen-based temperature-programmed reduction, and ammonia temperature-programmed desorption techniques. Among the Co-Zn-MMO catalysts, the Co1-Zn2-MMO catalyst, with a Co-to-Zn molar ratio of 1:2, exhibited the highest acidity, the largest pore size and pore capacity, and the highest density (65.56%) of Co2+δ-Ov-Zn2-δ oxygen vacancy. These characteristics resulted from the metal–support interaction effect, leading to superior HDO activity for guaiacol. Furthermore, the Co1-Zn2-MMO catalyst effectively removed heteroatomic components from larch wood-derived bio-oil, thereby enhancing the quality of the bio-oil product.

CoPMoV Sulfide Catalysts Supported on Natural Halloysite Nanotubes in Hydrotreating of Dibenzothiophene and Naphthalene

Mixed sulfided CoMo catalysts supported on γ-Al2O3 and halloysite nanotubes (HNTs) were synthesized by incipient wetness impregnation with salt solutions of Keggin-type phosphorus- and vanadium-containing heteropolyacids. The synthesized materials were characterized by low-temperature nitrogen adsorption, energy dispersive X-ray fluorescence analysis, temperature-programmed reduction (both for the oxide and sulfide catalysts), and Raman spectroscopy, and were tested in hydrogenation of naphthalene and hydrodesulfurization of dibenzothiophene. The HNT-supported catalyst exhibited a greater activity in these reactions.

A New Approach to the Preparation of Stable Oxide-Composite Cobalt–Samarium Catalysts for the Production of Hydrogen by Dry Reforming of Methane

A new approach to preparing a series of Co/Sm2O3 catalysts for hydrogen production by the dry reforming of methane has been developed. The catalyst precursors were synthesized with a simple method, including the evaporation of aqueous solutions of cobalt and samarium nitrates, followed by a short-term calcination of the resulting material. The as-prepared and spent catalysts were characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, temperature-programmed reduction, and thermogravimetric analysis. The content of cobalt in the synthesized materials affects their phase composition and carbonization resistance in the dry reforming of the methane reaction. It has been shown that preheating in N2 atmosphere produces catalysts that provide a stable yield of hydrogen and CO of 94–98% for at least 50 h at 900 °C. These yields are among the highest currently available for the dry reforming of methane catalysts made from Co-Sm complex oxides. It has been established that the decrease in the amount of cobalt in the catalyst and its preheating to an operating temperature of 900 °C in a nitrogen flow help to prevent the carbonization of the catalyst and the sintering of metal particles.

Microwave-assisted CO oxidation over LaNiO3 and Ce-promoted LaNiO3

Microwave-assisted catalytic reactions have been investigated for energy-efficient chemical processes. However, catalysts with comparatively high heating properties, activities, and economics have been developed with limited success. In this study, we investigated the catalytic properties of Ce addition to LaNiO3 catalyst, which has high CO oxidation activity and high microwave heating properties. Ce-added catalysts exhibited high heating properties under microwave heating. Increasing the Ce content in the catalyst enhanced the dielectric loss factor, the ability to absorb microwaves and convert them to heat, and improved the microwave heating properties of the catalyst. The catalytic activity toward CO oxidation over Ce-added catalysts decreased in the order of La0.8Ce0.2NiO3 > La0.9Ce0.1NiO3 > LaNiO3 at all oxygen partial pressures when compared to the same microwave power. To clarify the role of Ce addition, temperature programmed reduction (TPR) by H2, CO, and XAFS measurements were performed. TPR results suggested that Ce promotes oxygen mobility and then affects both CO oxidation and microwave heating properties.

Low temperature catalytic activity of hydrothermally synthesised ruthenium promoted ceria-zirconia composites for reforming CO2-rich methane

The use of CO2-rich natural gas as feedstock in DRM is an attractive route of carbon dioxide utilisation due to the compositional advantage of these particular resources. The optimal operating conditions would potentially improve the overall thermal efficiency of the DRM process, especially when the temperature is lower than 800 °C. This study reports a catalyst with the demonstrated high performance and high coke-resistance, developed from ruthenium modified ceria-zirconia. Coprecipitation and hydrothermal methods were adopted to prepare the ceria-zirconia supports, and then impregnated with a very small amount of Ru (0.10 wt%). The structure-catalytic activity relationship of the catalyst was further investigated in DRM. High conversions of CH4 and CO2, i.e., 44.0% and 57.4%, respectively, were achieved by using 0.1Ru1CZ5U-180 at low temperature of 600 °C. A significant reduction in the onset reaction temperature was observed from temperature programmed reduction (TPR) and this observation was related to the increased number of exchangeable oxygens in the presence of Ru. Nitrogen adsorption-desorption results suggested that the specific surface area and the total pore volume also improved the exchange of oxygen between adsorbed carbon dioxide molecules and the crystal lattice. It is evident that the presence of ruthenium accelerated the oxygen spillover process on the surface of the catalyst, and facilitated the dynamics of the oxygen exchange between the adsorbed carbon dioxide molecules and the ceria-zirconia, which ultimately contributed to the observed increase in catalytic activity at temperatures below 800 °C. Most importantly, no detectable carbon deposits were formed over the entire experimental period when the ruthenium modified ceria-zirconia catalyst was used.