Hydrogen Temperature-programmed Reduction Research Articles

Effect of Support on Stability and Coke Resistance of Ni-Based Catalyst in Combined Steam and CO2 Reforming of CH4.

Ni-based catalysts dispersed on different supports (MgO-α-Al2O3, CeO2, SBA-15, and MgO-SBA-15) were prepared by the impregnation method. Characteristics of the catalysts, including specific surface areas (N2 physisorption), crystalline phase compositions (powder X-ray diffraction, Raman spectroscopy), reducibility (hydrogen temperature-programmed reduction, H2-TPR), and morphology (scanning electron microscopy (SEM) and transmission electron microscopy, TEM)) were investigated. The activity and stability of the catalysts were tested for the combined steam and CO2 reforming of methane at 700 °C in a microflow system. The results show that the catalysts exhibit high activity in the BRM reaction. At 700 °C, the conversion of CH4 and CO2 reached 86–99% and 67–80%, respectively, in which the Ni/Mg–SBA catalyst is the best with conversions of CH4 and CO2 reaching 99% and 80%. Coke accumulation on the surface of the catalysts for 100 h time on stream (TOS) was evaluated by the temperature-programmed oxidation (TPO) technique. The major cause of the catalytic deactivation was elucidated by combining the determination of the amount and type of deposited coke with the changes in the physicochemical properties of the catalysts after the long-term reaction. Almost complete loss of activity was observed on Ni/Mg–Al catalyst after 100 h TOS, while the activity drop was slow on the Ni/Mg–SBA sample, about 15–20% of the total value. Otherwise, the Ni/CeO2 and Ni/SBA catalysts firmly retained their stable activity for 100 h TOS due to the minimal carbon deposition and stability of these catalysts’ structure. The highly considerable formation of inert Cγ carbon and sintering over Ni catalyst supported on MgO-α-Al2O3 were responsible for the lower stability of this catalyst compared to those supported on CeO2 and SBA-15.

Investigating the effects of synthesis procedures on textural and catalytic properties of nickel/magnesium silicate catalyst in glycerol dry reforming

• The synthesis method affects the structural properties of the Ni/MgO.SiO 2 catalyst. • The structural features of the Ni catalyst affect catalytic performance significantly. • The Ni/MgO.SiO 2 catalyst prepared by one-pot method showed better performance. • The one-pot method has resulted in the highest textural properties of the Ni/MgO.SiO 2. Ni-based catalysts supported on magnesium silicate were synthesized using various synthesis procedures and were then investigated for the first time in the glycerol-DR (dry reforming) process. In general, synthesis procedures for catalyst supports included co-precipitation and hydrothermal, and nickel as active metal was attached to the support simultaneously with support preparing and impregnation technique. The results of characterizations of Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), hydrogen temperature-programmed reduction (TPR-H 2 ), temperature-programmed oxidation (TPO), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) element mapping, Fourier transform infrared (FTIR), thermogravimetric analysis (TGA-DTA), and the catalytic glycerol-DR reaction tests illustrated that the preparation route of Ni/MgO.SiO 2 catalyst is effective in the structural and physicochemical features of the sample. It was observed that the catalysts with various synthesis methods exhibited different activity and stability during the glycerol-DR reaction. However, the highest glycerol conversion (31–50%) and the yield of both H 2 and CO were achieved over the Ni/MgO.SiO 2 (I) catalyst at all reaction temperature ranges (600–750 °C). The high catalytic performance of the Ni/MgO.SiO 2 (I) sample in the glycerol-DR reaction was related to its textural properties such as surface area (411 m 2 g −1 ), the crystallite size (8.5 nm), and active species dispersion, which were superior for this catalyst in comparison with other samples. This sample also exhibited better catalytic stability during the reaction. Furthermore, synthesis gas (syngas) was produced for all catalysts with an H 2 /CO ratio of less than 1.6. These results clearly show a significant impact of the sample synthesis procedure on the catalyst's final physical and chemical properties. The Ni/MgO.SiO 2 catalyst prepared with a one-step method showed high potential as a glycerol-DR catalyst for syngas production.

Component regulation in novel La-Co-O-C composite catalyst for boosted redox reactions and enhanced thermal stability in methane combustion

A novel La-Co-O-C (LC-C) composites were prepared via a facile co-hydrothermal route with oxides and glycerol and further optimized for methane catalytic activity and thermal stability via component regulation. It was demonstrated that Co3O4 phase was the main component in regulation. The combined results of X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption of oxygen (O2-TPD), temperature-programmed reduction of hydrogen (H2-TPR), temperature-programmed desorption of ammonia/carbon dioxide (NH3/CO2-TPD) revealed that component regulation led to more oxygen vacancies and exposure of surface Co2+, lower surface basicity and optimized acidity, which were beneficial for adsorption of active oxygen species and activation of methane molecules, resulting in the excellent catalytic oxidation performance. Especially, the (3.5)LC-C (3.5 is Co-to-La molar ratio) showed the optimum activity and the T50 and T90 (the temperature at which the CH4 conversion rate was 50% and 90%, respectively) were 318 and 367°C, respectively. Using theoretical calculations and in situ diffuse reflection infrared Fourier transform spectroscopy characterization, it was also found that the catalytic mechanism changes from the “Rideal-Eley” mechanism to the “Two-term” mechanism depending on the temperature windows in which the reaction takes place. Besides, the use of the “Flynn-Wall-Ozawa” model in thermoanalytical kinetics revealed that component regulation simultaneously optimized the decomposition activation energy, further expanding the application scope of carbon-containing composites.

Exploring the effect of calcination temperature and sulphuric acid impregnation treatment on the NH3-SCR activity of cold-rolled sludge

In recent years, sulphate materials have received more and more attention because of high activity in the selective catalytic reduction of nitrogen oxides with ammonia (NH3-SCR). In this paper, a series of catalysts for NH3-SCR were prepared by sulphuric acid impregnation and calcination at different temperatures of cold-rolled sludge which main component is iron oxide. The performance of cold-rolled sludge catalyst was measured by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), temperature programmed-reduction of hydrogen (H2-TPR), temperature programmed desorption of ammonia (NH3-TPD) and X-ray photoelectron spectroscopy (XPS). It was demonstrated that the increase of iron sulphate and Fe3+ content can be observed in the cold-rolled sludge after sulfuric acid impregnation and low temperature calcination (300 ℃), which leads to the improvement of SCR denitration performance. The results show that 100% denitration conversion can be achieved at 280 °C via the modified cold-rolled sludge, with 94% of the performance was retained after the introduction of SO2 and H2O for 5 h. There are minor morphological structural changes in the catalyst, while the redox properties and acidity of the catalyst changed significantly after the treatment process of sulfuric acid impregnation and calcination. This means that the enhanced redox properties and acidity of the catalyst play a key role in improving the activity of NH3-SCR.

Promotional effect of cobalt doping on catalytic performance of cryptomelane-type manganese oxide in toluene oxidation

The cryptomelane-type manganese oxide (OMS-2)-supported Co (xCo/OMS-2; x = 5, 10, and 15 wt.%) catalysts were prepared via a pre-incorporation route. The as-prepared materials were used as catalysts for catalytic oxidation of toluene (2000 ppmV). Physical and chemical properties of the catalysts were measured using the X-ray diffraction (XRD), Fourier transform infrared spectroscopic (FT-IR), scanning electron microscopic (SEM), X-ray photoelectron spectroscopy (XPS), and hydrogen temperature-programmed reduction (H2-TPR) techniques. Among all of the catalysts, 10Co/OMS-2 performed the best, with the T90%, specific reaction rate at 245°C, and turnover frequency at 245°C (TOFCo) being 245°C, 1.23 × 10−3 moltoluene/(gcat·sec), and 11.58 × 10−3 sec−1 for toluene oxidation at a space velocity of 60,000 mL/(g·hr), respectively. The excellent catalytic performance of 10Co/OMS-2 were due to more oxygen vacancies, enhanced redox ability and oxygen mobility, and strong synergistic effect between Co species and OMS-2 support. Moreover, in the presence of poisoning gases CO2, SO2 or NH3, the activity of 10Co/OMS-2 decreased for the carbonate, sulfate and ammonia species covered the active sites and oxygen vacancies, respectively. After the activation treatment, the catalytic activity was partly recovered. The good low-temperature reducibility of 10Co/OMS-2 could also facilitate the redox process accompanied by the consecutive electron transfer between the adsorbed O2 and the cobalt or manganese ions. In the oxidation process of toluene, the benzoic and aldehydic intermediates were first generated, which were further oxidized to the benzoate intermediate that were eventually converted into H2O and CO2.

Pd–Ni bimetallic nanoparticles supported on TiO2 as an efficient catalyst for catalytic transfer hydrodeoxygenation of guaiacol

Bio-oil is a sustainable energy source, produced from pyrolysis of lignocellulosic materials or algae. It is, however, difficult to directly use the bio-oil for fuels due to several drawbacks, such as its viscosities and high oxygen content. One of the ways to solve this is upgrading of the bio-oil through hydrodeoxygenation (HDO). In this study, guaiacol was used as a bio-oil model compound in HDO reaction via catalytic transfer hydrogenation. The reaction was conducted in the presence of TiO2-supported palladium catalysts, with isopropyl alcohol as a hydrogen source. Nickel and molybdenum were added into the Pd catalyst to investigate their effects on the catalyst activity. The prepared catalysts were characterized using XRD, N2 physisorption, hydrogen temperature-programmed reduction, and transmission electron microscopy. HDO reaction was carried out using a pressurized batch reactor at 250 °C for 1 h with 30 bar of helium. Liquid products were analyzed by GC–MS and GC–FID to identify and quantify the conversions and product yields. The result showed that the presence of nickel on the catalyst could improve the catalytic activity of Pd/TiO2. Guaiacol conversion over Pd–Ni/TiO2 was 32.2%, while the conversion of guaiacol over Pd/TiO2 was only 17.9%. In addition, Pd–Ni/TiO2 showed good selectivity to produce cyclohexanol, while Pd/TiO2 showed good selectivity to produce one oxygenated compound such as 2-methylphenol and phenol.

Fabrication of Pt-Loaded Catalysts Supported on the Functionalized Pyrolytic Activated Carbon Derived from Waste Tires for the High Performance Dehydrogenation of Methylcyclohexane and Hydrogen Production

The pyrolytic activated carbon derived from waste tires (PTC) was functionalized to fabricate the high performance of Pt-based catalysts in the dehydrogenation of methylcyclohexane and hydrogen production. Structural characterizations evidenced that the modification partially influenced the surface area, the pore structure, and the oxygen-containing functional groups of the supports. The techniques of CO pulse, transmission electron microscopy, and hydrogen temperature-programmed reduction were utilized to investigate the dispersion degrees and particle sizes of the active component Pt, and its interaction with the various functionalized supports, respectively. The results manifested that Pt particles loaded on the functionalized PTC-S had the largest dispersion degree and the smallest size among those loaded on PTC and other functionalized PTC (i.e., PTC-K and PTC-NH). Finally, the Pt-based catalysts were successfully applied in the dehydrogenation reaction of methylcyclohexane to yield hydrogen. The results revealed that the Pt catalyst over the functional PTC-S support exhibited a more excellent conversion of methylcyclohexane (84.3%) and a higher hydrogen evolution rate (991.5 mmol/gPt/min) than the other resulting Pt-based catalysts.

Highly Active Biphasic Anatase-Rutile Ni-Pd/TNPs Nanocatalyst for the Reforming and Cracking Reactions of Microplastic Waste Dissolved in Phenol.

Solvent-based recycling of plastic can offer the main improvement when it is employed for pyrolysis-catalytic steam reforming. In this research, plastic waste dissolved in phenol was used as a feed for catalytic cracking and steam reforming reactions for valuable liquid fuels and hydrogen production, which is gaining the attention of researchers globally. Microplastic wastes (MPWs) are tiny plastic particles that arise due to product creation and breakdown of larger plastics. They can be found mainly in several habitats, including seas and freshwater ecosystems. MPWs harm aquatic species, turtles, and birds and were chosen to recover in this study that can be reacted on the catalyst surface. Biphasic anatase-rutile TiO2 with spherical-shaped support for Ni and Pd metals with nanosized particles was synthesized via the hydrothermal treatment method, and its chemical and physical properties were characterized accordingly. According to temperature-programmed desorption of carbon dioxide (CO2-TPD) and temperature-programmed reduction of hydrogen (H2-TPR) results, the incorporation of Pd into Ni/TNPs enhanced the basicity of the support surface and the redox properties of catalysts, which were strongly linked to the improved hydrogen yield (71%) and phenol conversion (79%) at 600 °C. The Ni-Pd/TNPs nanocatalyst, with remarkable stability for 72 h of time on stream, is a promising catalyst for the MPW-phenol cracking and steam reforming reactions toward H2 production for clean energy generation and other environmental applications. Besides, this study has also highlighted the opportunities of overcoming the risk of microplastic waste and converting it into valuable fuels such as decamethyltetrasiloxane, phenanthrene, methyl palmitate, benzenepropanoic acid, benzoic acid, azulene, xanthene, anisole, biphenyl, phthalic acid, diisooctyl phthalate, etc.

Catalytic oleic acid hydrotreating to bio-aviation fuel over highly dispersed Ni/SAPO-11 catalysts prepared by citric acid and ethylene glycol co-assistance impregnation

A range of Ni/SAPO-11 catalysts was generated via citric acid impregnation using various solvents (water, ethanol, and ethylene glycol); these catalysts were employed to oleic acid hydrogenation for generating bio-aviation fuel. The catalysts were characterized through powder X-ray diffraction, low-temperature nitrogen adsorption–desorption, transmission electron microscopy, hydrogen temperature-programmed reduction, X-ray photoelectron spectroscopy, in-situ thermogravimetry-Fourier transform infrared, temperature-programmed desorption of ammonia, and pyridine-adsorbed infrared spectroscopy. It was observed that the type of solvent used for the preparation of catalysts influenced the Ni particle size of the catalysts. Notably, in the catalyst preparation process, citric acid as a chelating ligand and ethylene glycol as a solvent, can enhance the interaction between Ni and SAPO-11 support, leading to the formation of small nickel nanoparticles (6.7 nm), meantime with a large surface area and strong total acid content of 0.087 mmol/g. During oleic acid hydrogenation, the Ni/SAPO-11 catalyst with citric acid and ethylene glycol co-assistance impregnation exhibited excellent catalytic performance, with 99.9% conversion and 75.9% iso-alkanes (iso-C8-C18) selectivity. Particularly, to create more multibranched iso-alkanes and show stable catalytic performance after five runs.

Synergistic Effects of a CeO2/SmMn2O5-H Diesel Oxidation Catalyst Induced by Acid-Selective Dissolution Drive the Catalytic Oxidation Reaction.

A diesel oxidation catalyst (DOC) is installed upstream of an exhaust after-treatment line to remove CO and hydrocarbons and generate NO2. The catalyst should possess both good oxidation ability and thermal stability because it sits after the engine. We present a novel high-performance DOC with high steam resistance and thermal stability. A selective dissolution method is adopted to modify the surface physicochemical environment of CeO2-SmMn2O5. The X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, Raman, electron paramagnetic resonance, hydrogen temperature-programmed reduction, and temperature-programmed desorption results reveal that surface Sm cations are partially removed with the exposure of more Mn4+ and Ce3+ cations and the presence of active surface oxygen species. This mechanism benefits the oxygen transformation from Ce to Mn and promotes the Ce3+ + Mn4+ ↔ Ce4+ + Mn3+ redox cycle according to the in situ near-ambient pressure X-ray photoelectron spectroscopy and in situ diffuse reflectance infrared Fourier transformation spectroscopy results. Under laboratory-simulated diesel combustion conditions, the catalyst demonstrates excellent low-temperature oxidation catalytic activity (CO and C3H6 conversion: T100 = 250 °C) compared to a Pt-based catalyst (CO and C3H6 conversion: T100 = 310 °C) with a WHSV of 120,000 mL g-1 h-1. Specifically, NO conversion reaches 68% when the temperature is approximately 300 °C.

Co-production of hydrogen and carbon nanotubes by catalytic cracking of waste cooking oil model compound over Ni-Cu/Al-KCC-1

ABSTRACT Ni-Cu/Al-KCC-1 catalysts with different metal contents were prepared using fibrous nano-silica (Al-KCC-1) as a support. Field emission scanning electron microscopy observations showed that the spherical particle morphology and fibrous structure of the Al-KCC-1 were not changed after metal loading. Transmission electron microscopy images demonstrated that the introduction of copper improved the dispersion of the nickel, while X-ray diffraction and hydrogen temperature-programmed reduction confirmed the formation of a Ni-Cu alloy. The N2-Brunauer–Emmett–Teller specific surface areas of the catalysts were in the range of 269–378 m2/g and the average pore diameters were 7.988–12.078 nm. These Ni-Cu/Al-KCC-1 catalysts were used to promote the cracking of waste cooking oil model compound (WCOMC) to produce H2 and carbon nanotubes (CNTs), and the 10 wt% Ni-5 wt% Cu/Al-KCC-1 exhibited the highest catalytic activity. At a WCOMC flow rate of 0.04 mL/min and 750 °C, the instantaneous volume fraction of H2 reached 49.8 vol% and the content of H2 in the gaseous product was close to 71.4 vol%.

Ce-doping CuO/HZSM-5 as a regenerable sorbent for Adsorption–Oxidation removal of PH3 at low temperature

• Ce-doping Cu/HZSM-5 sorbents were synthesized and used for the removal of PH 3 . • Ce-doping can significantly enhance the adsorption capacity of the Cu/HZSM-5 sorbent. • The interaction between Ce and CuO improves the sorbent physicochemical properties. • The formation of phosphate/phosphide species resulted in the deactivation of sorbent. • The PH 3 capacity was preserved after three times thermal regeneration. A series Ce m Cu n O x /HZSM-5 sorbents were introduced to remove PH 3 in low-temperature and low-oxygen environments. The effects of copper loading and cerium doping on the adsorption–oxidation performance of the sorbents were investigated. Experimental results showed that doping with 1 wt% of cerium (Ce 1 Cu 30 O X /HZSM-5) could significantly improve the performance of the sorbent. The PH 3 breakthrough capacity was identified as 114.36 mg(PH 3 )•g sorbent -1 . In addition, after three thermal regeneration cycles, the sorbent still has ideal performance. X-ray diffractometer (XRD) and X-ray photoelectron spectroscopy (XPS) analyses exhibited that CuO was the main active species, and Ce-doping can increase the chemisorption oxygen on the surface of the sorbent. BET results demonstrated that the introduction of cerium could improve the specific surface area and pore volume of sorbent. Hydrogen temperature-programmed reduction (H 2 -TPR) and scanning electron microscope (SEM-EDS) indicated that cerium species played an important role in uniformly dispersing copper species on the HZSM-5 surface and improving the oxidation performance of sorbent. Moreover, the reaction products and mechanisms were also investigated by XRD, XPS, and in-situ FTIR spectra. The results indicated that the consumption of CuO and the accumulation of phosphorus species (e.g., P, P 2 O 5 , and Cu 3 P) on the surface and inner pores of the sorbent were the primary reasons for the deactivation of the sorbent.

Cu-cuprous/cupric oxide nanoparticles towards dual application for nitrophenol conversion and electrochemical hydrogen evolution

Herein, we synthesize a Cu-cuprous/cupric oxide-based family of catalysts via simple hydrothermal technique, and investigate the effect of copper oxide phases on the application of interest. These catalysts are applied towards dual application namely 4-nitrophenol (4-NP) conversion and electrochemical hydrogen evolution reaction (HER). Due to the difference in mechanism of these both applications, we pick up two best catalysts for either application. We explore these differences through intensive characterizations such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction of hydrogen(H2-TPR) analysis. XRD reveals the presence of varying copper oxide phases across all the synthesized catalysts. XPS discovers the disparities between catalysts annealed at various temperatures. Reducibility of catalysts is studied via H2-TPR since they can disclose phase conversions taking place in the material thereby directly affecting the application. Cu-Cu2O (150℃) could convert 98.6 % of 50 ppm 4-NP into 4-aminophenol (4-AP) with recycle tests up to 10 cycles yielding conversion values between 96.3 and 98.9% which are high enough for any catalyst to reach its maximum potential. CuO-Cu2O (300℃) exhibits best HER activity with the least onset potential of −0.28 V vs. RHE at 1 mA cm−2 possessing a maximum current density of 366 mA cm−2.

CO2 Methanation: Nickel-Alumina Catalyst Prepared by Solid-State Combustion.

The development of solvent-free methods for the synthesis of catalysts is one of the main tasks of green chemistry. A nickel–alumina catalyst for CO2 methanation was synthesized by solid-state combustion method using hexakis-(imidazole) nickel (II) nitrate complex. Using X-ray Powder Diffraction (XRD), Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Hydrogen temperature-programmed reduction (H2-TPR), it was shown that the synthesized catalyst is characterized by the localization of easily reduced nickel oxide on alumina surface. This provided low-temperature activation of the catalyst in the reaction mixture containing 4 vol% CO2. In addition, the synthesized catalyst had higher activity in low-temperature CO2 methanation compared to industrial NIAP-07-01 catalyst, which contained almost three times more hard-to-reduce nickel–aluminum spinel. Thus, the proposed approaches to the synthesis and activation of the catalyst make it possible to simplify the catalyst preparation procedure and to abandon the use of solvents, which must be disposed of later on.

Effect of the modification of alumina supports with chloride on the structure and catalytic performance of Ag/Al2O3 catalysts for the selective catalytic reduction of NOx with propene and H2/propene

The effect of the modification of an alumina support with chloride on the structure and the catalytic performance of Ag/Al2O3 catalysts (SA) was investigated for the selective catalytic reduction (SCR) of NO using C3H6 or H2/C3H6 as reductants. The Ag/Al2O3 catalyst and Cl−-modified Ag/Al2O3 catalysts (SA-Cl) were prepared by a conventional impregnation method and characterized by X-ray diffraction, Brunauer-Emmett-Teller isotherm analysis, electron probe microanalysis, transmission electron microscopy, UV-Vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, and hydrogen temperature-programmed reduction. The catalytic activities in the C3H6-SCR and H2/C3H6-SCR reactions were evaluated, and the reaction mechanism was studied using in situ diffuse reflectance infrared Fourier transform spectroscopy and synchrotron vacuum ultraviolet photoionization mass spectroscopy (SVUV-PIMS). We found that Cl− modification of the alumina-supported Ag/Al2O3 catalysts facilitated the formation of oxidized silver species (Agnδ+) that catalyze the moderate-temperature oxidation of hydrocarbons into partial oxidation products (mainly acetate species) capable of participating in the SCR reaction. The low-temperature promoting effect of H2 on the C3H6-SCR (“hydrogen effect”) was found to originate from the enhanced decomposition of strongly adsorbed nitrates on the catalyst surface and the conversion of these adsorbed species to –NCO and –CN species. This “H2 effect” occurs in the presence of Agnδ+ species rather than the metallic Ag0 species. A gaseous intermediate, acrylonitrile (CH2CHCN), was also identified in the H2/C3H6-SCR reaction using SVUV-PIMS. These findings provide novel insights in the structure-activity relationship and reaction mechanisms of the SA-catalyzed HC-SCR reaction of NO.

Regulation of Strong Metal-Support Interaction by Alkaline Earth Metal Salts.

Classical strong metal-support interaction (SMSI) is of significant importance to heterogeneous catalysis, where electronic promotion and encapsulation of noble metal by reducible support are two main intrinsic properties of SMSI. However, the excessive encapsulation will inevitably hamper the contact between active sites and reactant, leading to reduced activity in catalysis. Herein, alkaline earth metal salts are employed to depress the encapsulation of Ru nanoparticles in Ru/TiO2 catalyst in the present study. Thermodynamic calculation, transmission electron microscopy (TEM) and chemisorption results show that the alkaline earth metal salts could successfully prevent the migration of TiO2-x overlayer to Ru nanoparticles in Ru/TiO2 catalyst via in situ formation of titanates, resulting in high exposure of active metal. Meanwhile, X-ray photoelectron spectroscopy (XPS) and hydrogen temperature-programmed reduction (H2 -TPR) results reveal that an even stronger electron donation from the reduced support to Ru nanoparticles is achieved. As a result, the alkaline earth metal salts-doped Ru/TiO2 catalysts exhibit superior activity in catalytic hydrogenation of aromatics, which is in contrast to the pristine Ru/TiO2 catalyst that shows negligible activity under the same conditions due to the excess encapsulation of Ru nanoparticles in Ru/TiO2 catalyst.

MoOx-Decorated Co-Based Catalysts toward the Hydrodeoxygenation Reaction of Biomass-Derived Platform Molecules.

Catalytic conversion of a biomass derivative (levulinic acid, LA) to a high value-added product (γ-valerolactone, GVL) has attracted much attention, in which the control of catalytic selectivity plays an important role. Herein, a stepwise method was developed to prepare Co-MoOx catalysts via topological transformation (calcination reduction) from layered double hydroxide (Mo/CoAl-LDH) precursors. X-ray diffraction, high-resolution transmission electron microscopy, and hydrogen temperature-programmed reduction demonstrate the formation of MoOx-decorated Co structures of Co-MoOx samples. Remarkably, the sample that is reduced at 500 °C is featured with the most abundant interfacial Coδ+ (denoted as Co-MoOx-500), which exhibits an excellent catalytic performance toward the hydrodeoxygenation (HDO) reaction of several biomass-derived platform molecules (furfural, FAL; succinic acid, SA; 5-hydroxymethyl-furfural, HMF; and levulinic acid, LA). Especially, this optimal catalyst displays a high yield (99%) toward the HDO reaction of LA to GVL, which stands at the highest level among non-noble metal catalysts. The combination of in situ FT-IR characterization and theoretical calculation further confirms that interfacial Coδ+ sites in Co-MoOx-500 act as adsorption active sites for the polarization of a C═O bond in an LA molecule, which simultaneously promotes C═O hydrogenation and C-O cleavage. Moreover, the MoOx overlayer suppresses the formation of byproducts by covering the Co0 sites. This work offers a cost-effective and efficient catalyst, which can be potentially applied in catalytic conversion of biomass-derived platform molecules.

Pt-Modulated CuMnOx Nanosheets as Catalysts for Toluene Oxidation

Controllable ternary Pt–Cu–Mn lamellar oxides with different amounts of Pt were synthesized using a facile and expeditious self-propagating flaming technique for catalytic oxidation of toluene. The surface structure, composition, and structure–performance relationship were investigated by combining X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area, scanning electron microscopy (SEM), transmission electron microscopy (TEM), hydrogen temperature-programmed reduction (H2-TPR), and X-ray photoelectron spectroscopy (XPS). The catalytic performance of the as-produced catalysts toward the catalytic oxidation of toluene was investigated. Among the catalysts, the 0.5Pt-MnCu catalyst has shown 90% toluene removal at 228 °C with excellent cyclic stability, which is a significant achievement for MnCu binary nanosheet-like catalysts containing low amounts of Pt (0.5 wt %). This study has also inferred the degradation activity of modulated MnCu composite catalysts, which greatly hinges on the doping level of Pt. The lattice oxygen species are dominating according to the Mn–O bond strength, local environment, and reducibility. Moreover, Pt can increase the covalency of surface metal–oxygen bonds and electron affinity of surface metal-coordinated oxygen centers, thereby expediting the adsorption/activation of the gaseous oxygen molecules on oxide surfaces, which can step up the lattice oxygen as well as oxygen vacancy-involved reactions to invoke the Mars–van Krevelen and Langmuir–Hinshelwood mechanisms for boosting the overall toluene oxidation performance of PtCuMnOx catalytic materials. Based on the obtained results, this study proposes a vital insight into manipulating the nanoscale catalytic functions, which could also promise pivotal potential toward engineering the state-of-the-art transition-metal nanostructure for environmental catalysis.

CeO2- and CaO-Promoted Precipitation Method for One-Step Preparation of Vermiculite-Based Multilayer Mesoporous Ni-Based Catalysts for Dry Reforming of Methane.

In this paper, a molecular sieve (VSiO2) prepared from modified vermiculite is used as a support, and a multilayer mesoporous catalyst, Ni-VSiO2, is prepared while the active components are loaded in one step by the precipitation method. The catalyst is further modified by adding additives Ca and Ce to prepare the catalyst Ni-5x-VSiO2 (x = Ce, Ca) and is used for the dry reforming of methane reaction. The catalyst is characterized by X-ray fluorescence, Brunauer–Emmett–Teller analysis, scanning electron microscopy, hydrogen temperature-programmed reduction test, transmission electron microscopy, thermogravimetric analysis, and other technical means. The result shows that under a normal pressure of 750 °C, the catalyst Ni-Ca-VSiO2 has good stability. The catalyst Ni-Ce-VSiO2 has good activity, stability and carbon deposition resistance, and the conversion rates of CO2 and CH4 are 88% and 78%, respectively. This is because the mesoporous structure allows Ni nanoparticles to enter the pores of the catalyst support, thereby inhibiting the aggregation of the active component Ni and improving its sintering resistance. CeO2 additives provide more oxygen vacancies to inhibit the formation of carbon deposits. At the same time, the strong interaction between the active component Ni and the additive CeO2 is also beneficial to improve its sintering resistance.

Synergistic Effects of Co3O4-CeO2 Nanoparticles towards Catalytic Oxidation of Aromatic Hydrocarbons: A Study in Association with Carbon Monoxide and Humidity

In this study, a series of Co3O4-CeO2 nanocomposites with various Co3O4 loading were fabricated by the impregnation method using cobalt(II) acetate as the cobalt precursor for the treatment of benzene, toluene, ethylbenzene, and xylene (BTEX). The as-prepared Co3O4-CeO2 nanocomposites were thoroughly characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Brumauer-Emmett-Teller (BET), hydrogen temperature-programmed reduction (H2-TPR), and temperature-programmed desorption (O2-TPD). The excellent reproduction of active oxygen species caused by the high dispersion of Co3O4 crystals on the CeO2 supports was established. In addition, the reduction peaks of Co3O4-CeO2 nanocomposites were found at much lower temperatures compared to pure CeO2, considering their unique redox property influencing on the high catalytic activity. Among the characterized materials, the 5.0 wt.% Co3O4 supported on CeO2 (5.0Co–Ce) was the best system for catalytic oxidation of xylene, along with excellent performances in the cases of benzene, ethylbenzene, and toluene. Its catalytic activity increased in the order: benzene < xylene < ethylbenzene < toluene . Furthermore, the addition of carbon monoxide (CO) as a coreactant permitted to improve the catalytic performances in such oxidations as well as the stability of as-prepared catalysts, even under humid conditions.