Catalyst For Formation Research Articles

Defective Graphene on the Transition-Metal Surface: Formation of Efficient Bifunctional Catalysts for Oxygen Evolution/Reduction Reactions in Alkaline Media.

Supported single-atom catalysts (SACs) have attracted enormous attention because of their high selectivity, activity, and efficiency, compared to conventional nanoparticles and metal bulk catalysts. However, all of these unique merits rely on the stability of the SAC, as reported by many investigators. To avoid aggregation of single-metal atoms and maintain the high performance of the SAC, various substrates have been tried to support them, particularly on graphene nanosheets. A spontaneous interface phenomenon between graphene and the Co (and Ni) substrate discovered in this work is that the holes in the graphene layer can stimulate metal atoms to pop up from a metal substrate and fill the double vacancy in graphene (DV-G) and stabilize on the graphene surface. The unique structure of the lifted metal atom is expected to be useful for the bifunctional SAC for electrocatalytic oxygen evolution reactions (OERs) and oxygen reduction reactions (ORRs). Our first-principles calculations indicate that the DV-G on the Co(0001) surface can serve as an excellent bifunctional OER/ORR catalyst in alkaline media with extremely low overpotentials of 0.39 V for OER and only 0.36 V for ORR processes, which are even lower than those for previously reported bifunctional catalysts. We believe that the catalytic activity stems from the interface coupling effect between the DV-G and metal substrate, as well as the charge redistribution in the graphitic sheet.

Preparation of carbonaceous solid acid catalyst from Acacia mangium wood sawdust for conversion of same source into 5-hydroxymethylfurfural

ABSTRACTA carbon-based solid acid catalyst was prepared by incomplete carbonization of Acacia mangium wood sawdust, treated with H3PO4 followed by sulfonation. FT-IR, BET, SEM, EDS and TPD-NH3 were used to characterize the structure and performance of the catalyst. Results showed that the catalyst formed was an amorphous carbon composed of aromatic carbon sheets with –COOH, –OH and –SO3H groups. Primary impregnation with H3PO4 could promote formation of mesoporous catalyst. The optimized carbonization temperature and time for the catalyst were 500°C and 30 min. The –SO3H density and specific surface area for the catalyst prepared under the optimized conditions were about 2.9–3.2 mmol/g and 740 m2/g, respectively. The A. mangium wood sawdust was also used to produce hydroxymethylfurfural, utilizing the prepared solid catalyst. The biomass was pretreated by alkaline solution to obtain the pulp, which was saccharified by Novozymes commercial enzyme and then used for the conversion. The integrated scheme for the preparation of the solid acid catalyst and hydroxymethylfurfural from A. mangium wood is an efficient conversion method of wood biomass into green catalysts and chemicals.

Electro-oxidation of ethylene glycol on Pt[sbnd]Co metal synergy for direct ethylene glycol fuel cells: Reduced graphene oxide imparting a notable surface of action

Slow electro-oxidation reaction and low power output are two major limiting factors in successful commercialization of fuel cell technology. An efficient and stable electro-catalyst with effectual metal combination supported on a durable matrix may provide a viable solution to overcome these issues. The direct ethylene glycol fuel cell consisting of bimetallic anode catalysts are expected to lead out the high-power output issues. In the present paper, we emphasized on the synthesis of a high performing CO poisoning resistant Pt based binary anode catalysts for the electro-oxidation of ethylene glycol (EG) using a chemical reduction route. The electrocatalysts consists of PtCo alloy nanoparticles with different composition of Pt and Co, supported on reduced graphene oxide (rGO). Physical characterizations revealed the formation of bi-metallic catalysts within the size ranges from 2 nm to 3 nm. Electrochemical analysis revealed that PtxCoy/rGO electrocatalyst with x: y molar ratio of 1:9 imparts the highest peak current and power density as compared to commercially available Pt/C and PtCo/C anode catalysts for ethylene glycol electro-oxidation. The power density (81.1 mW/cm2) obtained using PtxCoy/rGO with x:y molar ratio of 1:9 metal catalyst in DEGFC is more than other synthesized catalysts at an operating temperature of 100 °C and the operating pressure of 1 bar with 2 M ethylene glycol as anode fuel and anode and cathode platinum metal loading of 2 mg/cm2.

The Effect of the Precursor Solution’s Pretreatment on the Properties and Microstructure of the SCS Final Nanomaterials

Nanostructured nickel-based catalysts were produced by solution combustion synthesis and it was found that their properties and structure depended on the pretreatment of the precursor solution. X-ray diffraction, N2 adsorption, and an infrared high-speed camera were used to follow the various synthesis steps and to characterize the obtained catalysts, while their catalytic activity was determined in the hydrogenation of maleic acid. It was determined that the amount of water used and the heating of the precursor solution under mild stirring up to 70 °C influenced the nickel nitrate–glycine–water complexes that were formed in the precursor solution in the form of dendrites. These play a key role in the solution combustion synthesis (SCS) reaction mechanism and in particular in the formation of nickel-based catalysts. Understanding the interrelationships between the processing parameters and the ensuing powder properties allowed an efficient optimization of the catalytic performance.

Novel magnetic nanoparticles with morpholine tags as multirole catalyst for synthesis of hexahydroquinolines and 2-amino-4,6-diphenylnicotinonitriles through vinylogous anomeric-based oxidation

A new heterogeneous nanomagnetic catalyst bearing morpholine tags was synthesized and characterized. The formation of the nanomagnetic catalyst was fully confirmed by several methods, including Fourier-transform infrared (FT-IR) spectroscopy, energy-dispersive X-ray (EDX) spectroscopy, elemental mapping, X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetry/derivative thermogravimetry (TG/DTG), and vibrating-sample magnetometry (VSM). The catalytic performance of the novel nanomagnetic catalyst was examined in multicomponent preparation of hexahydroquinolines and 2-amino-4,6-diphenylnicotinonitriles through vinylogous anomeric-based oxidation under mild reaction conditions. Novel magnetic nanoparticles with morpholine tags promoted synthesis of hexahydroquinolines and 2-amino-4,6-diphenylnicotinonitriles through vinylogous anomeric-based oxidation.

Pt/CeO2 and Pt/CeSnOx Catalysts for Low-Temperature CO Oxidation Prepared by Plasma-Arc Technique.

We applied a method of plasma arc synthesis to study effects of modification of the fluorite phase of ceria by tin ions. By sputtering active components (Pt, Ce, Sn) together with carbon from a graphite electrode in a helium ambient we prepared samples of complex highly defective composite PtCeC and PtCeSnC oxide particles stabilized in a matrix of carbon. Subsequent high-temperature annealing of the samples in oxygen removes the carbon matrix and causes the formation of active catalysts Pt/CeOx and Pt/CeSnOx for CO oxidation. In the presence of Sn, X-Ray Diffraction (XRD) and High-Resolution Transmission Electron Microscopy (HRTEM) show formation of a mixed phase CeSnOx and stabilization of more dispersed species with a fluorite-type structure. These factors are essential for the observed high activity and thermic stability of the catalyst modified by Sn. X-Ray Photoelectron Spectroscopy (XPS) reveals the presence of both Pt2+ and Pt4+ ions in the catalyst Pt/CeOx, whereas only the state Pt2+ of platinum could be detected in the Sn-modified catalyst Pt/CeSnOx. Insertion of Sn ions into the Pt/CeOx lattice destabilizes/reduces Pt4+ cations in the Pt/CeSnOx catalyst and induces formation of strikingly high concentration (up to 50% at.) of lattice Ce3+ ions. Our DFT calculations corroborate destabilization of Pt4+ ions by incorporation of cationic Sn in Pt/CeOx. The presented results show that modification of the fluorite lattice of ceria by tin induces substantial amount of mobile reactive oxygen partly due to affecting geometric parameters of ceria by tin ions.

Pd(II), Cu(II), and pillared clay based nanocatalysts for low-temperature CO oxidation

Pillared clays (PILCs) are little-studied as supports in compositions of anchored metal complex catalysts. In the work, pillared clay, Al-PILC, was prepared by using Ukrainian natural bentonite, N-Bent, and the aluminum polycation, [Al13O4(OH)24(H2O)12]7+ (Al13), as an intercalating agent. The final product was used for preparing К2PdCl4–Cu(NO3)2–KBr/Al-PILC nanocatalysts by an impregnation method. Initial N-Bent and Al-PILC as well as the nanocompositions based on them were characterized by XRD, FT-IR spectroscopy, DTG–DTA, water vapor adsorption, and pH metry. К2PdCl4–Cu(NO3)2–KBr/ $${\bar{\text{S}}}$$ compositions ( $${\bar{\text{S}}}$$ were N-Bent or Al-PILC) were tested in the reaction of CO oxidation with air oxygen at temperature of 20 °C and a relative humidity of 67%. It has been found that the preliminary modification of natural bentonite by Al13 intercalation results in formation of the nanostructured catalyst with a crystallite size of 19 nm showing the maximum activity in the reaction under study at CPd(II) = 2.72 × 10−5 mol/g and copper(II) concentrations of 2.9 × 10−5 and 5.9 × 10−5 mol/g.

Influence of the Method of Boron Introduction on the Formation and Activity of Hydrotreatment Catalysts

Experimental data on the effect of the method of introducing boron and Ni(Co) and Mo compounds on the physicochemical properties and hydrodesulfurization activity of catalysts in the hydrotreatment of straight-run diesel fraction are presented. The dependence of the hardness of grains, their specific surface area, spectral and microstructural characteristics on the method of preparation of catalyst samples containing 0.7–0.8 wt % B2O3 was determined.

Room temperature CO2 reduction to solid carbon species on liquid metals featuring atomically thin ceria interfaces

Negative carbon emission technologies are critical for ensuring a future stable climate. However, the gaseous state of CO2 does render the indefinite storage of this greenhouse gas challenging. Herein, we created a liquid metal electrocatalyst that contains metallic elemental cerium nanoparticles, which facilitates the electrochemical reduction of CO2 to layered solid carbonaceous species, at a low onset potential of −310 mV vs CO2/C. We exploited the formation of a cerium oxide catalyst at the liquid metal/electrolyte interface, which together with cerium nanoparticles, promoted the room temperature reduction of CO2. Due to the inhibition of van der Waals adhesion at the liquid interface, the electrode was remarkably resistant to deactivation via coking caused by solid carbonaceous species. The as-produced solid carbonaceous materials could be utilised for the fabrication of high-performance capacitor electrodes. Overall, this liquid metal enabled electrocatalytic process at room temperature may result in a viable negative emission technology.

Visualizing Formation of Intermetallic PdZn in a Palladium/Zinc Oxide Catalyst: Interfacial Fertilization by PdHx.

Controllable synthesis of well-defined supported intermetallic catalysts is desirable because of their unique properties in physical chemistry. To accurately pinpoint the evolution of such materials at an atomic-scale, especially clarification of the initial state under a particular chemical environment, will facilitate rational design and optimal synthesis of such catalysts. The dynamic formation of a ZnO-supported PdZn catalyst is presented, whereby detailed analyses of in situ transmission electron microscopy, electron energy-loss spectroscopy, and in situ X-ray diffraction are combined to form a nanoscale understanding of PdZn phase transitions under realistic catalytic conditions. Remarkably, introduction of atoms (H and Zn in sequence) into the Pd matrix was initially observed. The resultant PdHx is an intermediate phase in the intermetallic formation process. The evolution of PdHx in the PdZn catalyst initializes at the PdHx /ZnO interfaces, and proceeds along the PdHx ⟨111⟩ direction.

Identification of Surface Structures in Pt3Cr Intermetallic Nanocatalysts

A precise understanding of the catalytic surface of nanoparticles is critical for relating their structure to activity. For silica-supported Pt–Cr bimetallic catalysts containing nominal Cr/Pt molar ratios of 0, 1.9, and 5.6, a fundamental difference in selectivity was observed as a function of composition for propane dehydrogenation, suggesting different surface structures. The formation of bimetallic catalysts and the phases present were confirmed by synchrotron in situ X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) of the nanoparticle as a function of reduction temperature. With the increasing reduction temperature, there is a systematic increase in the Pt LIII edge X-ray absorption near edge structure (XANES) energy, which is consistent with the incorporation of more metallic Cr into the nanoparticles. Pt LIII edge extended X-ray absorption fine structure (EXAFS) shows that the nanoparticles are Pt rich regardless of the reduction temperature, and XRD shows the presence of both Pt and Pt3Cr phases at temperatures below about 700 °C. For the latter, a full Pt3Cr intermetallic alloy forms after reduction at 800 °C. This work also presents a method for the characterization of the catalytic surface by the analysis of XAS difference spectra and XRD difference patterns of the (reduced and oxidized) catalysts. The surface analysis suggests that Pt3Cr formation begins at the surface, and at low reduction temperatures, a core–shell morphology is formed containing a Pt core with a Pt3Cr surface. By combining the XAS and XRD analyses with transmission electron microscopy (TEM) particle sizes, the thickness of the shell can be approximated. All evidence indicates that the shell thickness increases with the increasing reduction temperature until a full alloy is formed after reduction at about 800 °C but only if there is enough Cr2O3 available near Pt nanoparticles to form Pt3Cr. Catalysts containing a full monolayer coverage of Pt3Cr have higher olefin selectivity (>97%) compared with partially covered Pt surfaces (88%).

Tuning Catalytic Properties of Supported Bimetallic Pd/Ir Systems in the Hydrogenation of Cinnamaldehyde by Using the “Water-in-Oil” Microemulsion Method

Supported Pd/Ir bimetallic catalysts were synthesized by the “water-in-oil” microemulsion method at different precursor concentrations and characterized by XRD, XPS, SEM, TEM, and cyclic voltammetry. Depending on the preparation conditions, formation of bimetallic catalysts with different metal segregation and surface composition can be easily obtained, thus tuning the bimetallic structure of catalysts as well as their relative catalytic properties. Bimetallic Pd/Ir systems were efficiently tested in the hydrogenation of cinnamaldehyde showing a better performance than analogous monometallic catalysts.

Improved Cu- and Zn-based catalysts for CO2 hydrogenation to methanol

Abstract In this study the influence of metal dispersion, spinel formation, and surface properties of binary and ternary catalysts (CuO CeO2, ZnO CeO2, CuO ZnO CeO2, and CuO ZnO Al2O3) was evaluated. The catalysts prepared by polyol method using polyethylene glycol as a solvent have been tested in the CO2 hydrogenation to methanol performed at atmospheric pressure. The catalysts prepared by polyol method presented improved properties in terms of metal oxide dispersion, morphology (i.e. sponge-like shape for the CeO2-containing catalysts), and a large variety of metal and metal oxide species on the surface. Moreover, the CuO ZnO CeO2 and CuO ZnO Al2O3 catalysts exhibited a higher activity and selectivity in the methanol synthesis by CO2 hydrogenation than those displayed by catalysts prepared by more conventional methods.

Cofactor Controlled Encapsulation of a Rhodium Hydroformylation Catalyst

AbstractSupramolecular approaches in transition‐metal catalysis, including catalyst encapsulation, have attracted considerable attention. Compared to enzymes, supramolecular catalysts in general are less complex. Enzyme activity is often controlled by the use of smaller cofactor molecules, which is important in order to control reactivity in complex mixtures of molecules. Interested in increasing complexity and allowing control over supramolecular catalyst formation in response to external stimuli, we designed a catalytic system that only forms an efficient supramolecular complex when a small cofactor molecule is added to the solution. This in turn affects both the activity and selectivity when applied in a hydroformylation reaction. This contribution shows that catalyst encapsulation can be controlled by the addition of a cofactor, which affects crucial catalyst properties.

Cofactor Controlled Encapsulation of a Rhodium Hydroformylation Catalyst.

Supramolecular approaches in transition‐metal catalysis, including catalyst encapsulation, have attracted considerable attention. Compared to enzymes, supramolecular catalysts in general are less complex. Enzyme activity is often controlled by the use of smaller cofactor molecules, which is important in order to control reactivity in complex mixtures of molecules. Interested in increasing complexity and allowing control over supramolecular catalyst formation in response to external stimuli, we designed a catalytic system that only forms an efficient supramolecular complex when a small cofactor molecule is added to the solution. This in turn affects both the activity and selectivity when applied in a hydroformylation reaction. This contribution shows that catalyst encapsulation can be controlled by the addition of a cofactor, which affects crucial catalyst properties.

Sulfur‐Rich Colloidal Nickel Sulfides as Bifunctional Catalyst for All‐Solid‐State, Flexible and Rechargeable Zn‐Air Batteries

AbstractEarth‐abundant and high‐performance catalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are highly desirable in development of energy‐efficient rechargeable Zn‐air batteries. In this work, sulfur‐rich colloidal nickel sulfides (NiSx) are prepared as OER/ORR bifunctional catalysts via a two‐step hydrothermal process. The NiSx nanoparticles (NPs) with large surface area show high OER activity and excellent stability, as evidenced by low overpotential of 301 mV, small Tafel slope of 41 mV dec−1 and high stability over 20 h of chronopotentiometry test. Due to their sulfur‐rich nature (i. e. Ni3S4 and NiS2), the obtained NiSx also exhibit good ORR activity. The introduction of graphene oxide (GO) in the starting materials leads to the formation of a composite catalyst composed of conductive sulfur‐doped reduced graphene oxide (S‐rGO) and NiSx. A high ORR onset potential of 0.91 V (vs. RHE) is obtained from the sulfur‐rich NiSx NPs coupled with the S‐rGO which facilitates the electron‐transfer and furnishes the bifunctional catalytic activity. Rechargeable Zn‐air batteries with NiSx/S‐rGO bifunctional catalyst deliver stable charge and discharge voltages of 2.1 and 1.1 V over 590 cycles. Furthermore, all‐solid‐state and foldable Zn‐air batteries using pliable and robust air cathodes of NiSx/S‐rGO show similar voltage profile as their non‐foldable counterparts. The foldable batteries exhibit stable cycling performance for up to 120 discharge/charge cycles at either flat or folded state, proving their high electrochemical and mechanical stability.

Catalytic performance of Ni supported on ZnO‐Al2O3 composites with different Zn content in methane dry reforming

AbstractBACKGROUNDBecause of increasing environmental contaminations, hydrogen has attracted much attention as an effective and clean energy source. In addition, hydrogen and syngas are raw materials used in the production of valuable compounds. Methane dry reforming is one common method for syngas production. In this work, Ni catalysts supported on different ZnO–Al2O3 composite oxides were prepared. The effects of variation in Zn/Al ratio (Zn/Al = 0, 0.33, 0.5, 1, 2 and 3) on physico‐chemical properties and their activity and stability in methane dry reforming were investigated.RESULTSThe results indicated that Zn addition led to decreasing surface area, weakening the interaction between active phase and support, improving Ni reduction and therefore enhancing initial activity.CONCLUSIONWhen Zn content was low or just enough to produce ZnAl2O4 phase, only metallic Ni particles were detected after reaction which led to carbon filaments formation and deactivation of catalysts. Increasing Zn content formed NiZn alloy that played essential roles in activity and stability. High amounts of Zn (Zn/Al = 3) did not favor promoting effects due to the increasing active phase sizes and decreasing contact area. Ni/ZnO–Al2O3 with Zn/Al = 2 exhibited the highest activity and stability in methane dry reforming. © 2018 Society of Chemical Industry

Steam Reforming of Tar Using Low-Grade Iron Ore for Hydrogen Production

In the gasification process, tar material may cause operational problems, such as carbon deposition over a catalyst, pipe plugging, condensation, and tar aerosol formation. Unusual approaches shoul...

Synthesis of Bi2WO6 photocatalyst modified by SDBS and photocatalytic performance under visible light

Bismuth tungstate (Bi2WO6) photocatalysts, which modified with different ratios of sodium dodecyl benzene sulfonate (SDBS) and with enhanced visible light-driven activity, were synthesized by a facile solvothermal process. The photocatalysts were characterized by X-ray diffraction, scanning electron and transmission electron microscopies, and X-ray photoelectron and ultraviolet–visible diffuse reflectance spectroscopies. SDBS addition was found to control particle morphology and improve photocatalytic activity of Bi2WO6 catalysts. The solvent-thermal reaction time was critical in determining the catalysts’ structures and shapes and optimal at 16 h. Photocatalytic activities of SDBS–Bi2WO6 were determined by photocatalytic degradation of tetracycline (TC) in aqueous solution under visible light irradiation. Optical properties and TC degradation tests showed these SDBS–Bi2WO6 catalysts to exhibit enhanced visible light-driven photodegradation for TC. The photocatalytic activity for TC degradation was maximized at 90.39% after 90 min at 1.0 wt% SDBS dosage. In addition, the possible mechanisms for catalyst formation and photocatalytic degradation were discussed.

Heterogeneous Metal-Organic-Framework-Based Biohybrid Catalysts for Cascade Reactions in Organic Solvent.

In cooperative catalysis, the combination of chemo- and biocatalysts to perform one-pot reactions is a powerful tool for the improvement of chemical synthesis. Herein, UiO-66-NH2 was employed to stepwise immobilize Pd nanoparticles (NPs) and Candida antarctica lipase B (CalB) for the fabrication of biohybrid catalysts for cascade reactions. Distinct from traditional materials, UiO-66-NH2 has a robust but tunable structure that can be utilized with a ligand exchange approach to adjust its hydrophobicity, resulting in excellent catalyst dispersity in diverse reaction media. These attractive properties contribute to the formation of MOF-based biohybrid catalysts with high activity and selectivity in the synthesis of benzyl hexanoate from benzaldehyde and ethyl hexanoate. With this proof-of-concept, we reasonably expect that future tailor-made MOFs can combine other catalysts, ranging from chemical to biological catalysts for applications in industry.