Coke inhibition is one of the key issues for hydrocarbon fuel cracking. In the work reported in this paper, controllable cracking with greatly reduced coke deposits has been realized by the addition of a little ethanol over a bifunctional coating. The coating, consisting of perovskite and phosphotungstic acid, is prepared in a nickel-based super alloy tube reactor (diam. 3 mm × 0.5 mm × 1000 mm) by the wash-coating method. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy, and X-ray diffraction are utilized to characterize the morphology and phase composition of the coating and cokes. The results show that BaWO4, BaCeO3, SiO2, and H3PW12O40 coexist in the 4.2 μm coating with a uniform distribution. The anti-coking tests were conducted during the supercritical thermal cracking of RP-3 Chinese jet fuel with a flow rate of 1 g/s for 30 min at 700 °C and 4 MPa. The results show that the efficiency of coke inhibition reaches up to 96%, and the stability (i.e., pressure drop of tube reactor and cooler) of the system has been effectively improved. The deposited cokes were characterized by temperature-programmed oxidation and SEM. The pyrolysis products, including gas and liquid, were also analyzed. The results indicate that the strategy based on ethanol and a bifunctional coating not only plays an important role in eliminating the coke deposits on the reactor tube walls but also reduces the amount of typical coke precursors related to the aromatic condensation cokes. A possible mechanism for the process has been proposed. In general, phosphotungstic acid in the coating is capable of catalyzing the dehydration of ethanol for the production of water. Meanwhile, the perovskite structures can remove coke deposits on the coating through carbon–steam gasification reaction.

Metal-support interaction and corresponding interface regulation are of great importance for the preparation of well-defined, supported metal catalysts with outstanding performance. Herein a joint experimental-theoretical study has been conducted to investigate the role of polydopamine (PDA) as an interface facilitator for supported noble metal catalysts. The effects of PDA between various noble metals (Pt, Pd, Au, Ag) and a support (SBA-15) have been systematically investigated in the model reaction of 4-nitrophenol (4-NP) reduction by NaBH4. Based on the kinetic model of 4-NP reduction by NaBH4 and a set of density functional theory calculations on different 4-NP binding energies, a volcano-shaped relationship plot is obtained. The volcano-shaped dependence of the reaction rate constant on 4-NP adsorption energy is observed for supported noble metal catalysts with/without PDA. The general relationship indicates that PDA can effectively improve catalytic performance via adjusting 4-NP adsorption energy to a more suitable value. The results of charge density difference and Bader charge analysis illustrate the establishment of an ‘electron pool’ by PDA in the system to achieve controllable electronic charge redistribution for an optimized binding when the reactant molecule adsorbs on the metal nanoparticle.

•A joint experimental-theoretical investigation on alkylation over HPW.•Kinetic study on the formations of cyclohexyltoluene isomers has been conducted.•Reaction mechanism has been demonstrated by DFT calculation.•Product selectivity has been explained experimentally and theoretically.CC bond formation between an aromatic ring and cyclohexene is of great importance for the preparation of bicyclic hydrocarbons. In this work, alkylation of toluene with cyclohexene over phosphotungstic acid (HPW) has been investigated using both experimental reaction kinetics and ab initio density functional theory (DFT) methods. Kinetic models for the formations of o-cyclohexyltoluene, m-cyclohexyltoluene and p-cyclohexyltoluene have been established and used to fit the experimental kinetic data. The reaction rate constants and apparent activation energies for the formation of the three products have been calculated and compared. Based on DFT calculation, the energy profiles with relevant equilibrium and transition states have been determined for the adsorption of reactants, formation & deprotonation of the metastable states and desorption of the products. A metastable state of an adsorbed arenium ion on HPW has been demonstrated. The rate constants (k) for the major elementary steps at different temperatures have been calculated using DFT data. The apparent rate constants are further determined theoretically based on kinetic analysis. Results show that the theoretical calculation fits well with experimental data, both of which have similar tendency changing with temperature. Combined experimental kinetic results and DFT calculations suggest that both the formation and deprotonation of the metastable state play key roles in affecting the product selectivity.Download high-res image (179KB)Download full-size image

In this work, polydopamine (PDA)-coated multi-walled carbon nanotubes (CNTs) have been employed as reactive platforms for the anchoring of multiple heteroatom dopants. Single-, double-, and triple-doped CNTs with the elements N, S and B have been successfully prepared and systematically investigated as electrocatalysts for the oxygen reduction reaction (ORR). The obtained catalysts have been fully characterized by the nitrogen-adsorption technique, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Combining with the physicochemical properties of different doped CNTs and their catalytic performance, various doping modes are compared and the mechanism of these processes has been investigated. The synergetic effects on double and triple doped CNTs with N, S, and B are found. The new non-metal catalyst N–S–B-CNTs exhibits high electrocatalytic activity and good stability for ORR.

The formation of nanocomposites by embedding inorganic nanoparticles (NPs) in polymer brushes has been studied extensively for the development of functional surfaces. Polymer brushes are particularly useful matrices for the preparation of nanocomposites, because the macromolecular matrix acts as a reaction chamber for nanoparticle synthesis, as a scaffold for immobilization, and as a capping agent for preventing nanoparticle aggregation. Moreover, synergies between the polymer chains and the inorganic NPs will grant the composite new properties. The stimuli-responsive polymers/NPs endow the composites with excellent properties for many applications, such as in sensors, detectors, and electronic/optical devices. We tackle in this review the use of a subset of polymer brushes (e.g., polyelectrolytes and polyampholytes) for the embedment of inorganic NPs to make composite surfaces/NPs with specific functions.

Catalytic steam reforming of long-chain hydrocarbons has drawn great attention for hydrogen production or heat removement, which can be used for on-board/on-site fuel cell or hypersonic vehicle thermal protection. In this study, a series of Ni–Co bi-metal catalysts supported on Al2O3 with different ceria loadings have been prepared by a two-step impregnation method. Physical states and chemical properties of the as-synthesized catalysts have been characterized by XRD, nitrogen adsorption–desorption, H2-TPR and TEM. Steam reforming of n-dodecane has been carried out to evaluate catalytic performance of the obtained catalysts at 700 °C and atmospheric pressure in a fixed-bed tubular reactor. Both effects of CeO2 addition and Ni–Co alloying have been investigated to enhance catalytic activity and stability. After optimization, the catalyst promoted by 5 wt% ceria (NC/5CeAl) exhibits the highest conversion of n-dodecane (89 %) and the lowest coke deposition (reduced by 50 % compared with the one without ceria loading). The improvement in the performance of n-dodecane steam reforming is ascribed to the reduction of Ni particle size on alumina and the acceleration of coke gasification via redox, which has been achieved by Ni–Co alloying and CeO2 promotion.

Mussel-inspired polydopamine (PDA) particles with the size of ∼270 nm are used as a support of palladium (Pd) nanoparticles (NPs) for catalyst preparation. The surface morphology of the PDA particle has been modified via corrosion of CF3COOH. Surface chemistry of the obtained PDA particle has been engineered by the formation of a carboxylic acid-terminated alkanethiol monolayer. The obtained self-assembled monolayer-modified PDA (SAM-PDA) particles are used to load Pd NPs by simply adding H2PdCl4 solution to a suspension of SAM-PDA particles at room temperature. Transmission electron microscopy, energy-dispersive X-ray mapping, dynamic light scattering, X-ray diffraction, X-ray photoelectron spectroscopy, UV–vis, and Fourier transform infrared are used to characterize the catalyst and to investigate the process. Uniform Pd NPs (2–3 nm) have been well-dispersed on the SAM-PDA particles via controllable surface engineering. Surface charges and interactions with a metal ion are regulated by the monolayer of carboxylic acids. The surface chemistry of PDA particles has been finely engineered for efficient loading of noble metal NPs. The obtained Pd/SAM-PDA catalyst has shown greatly increased activity and good reusability compared with Pd/PDA in the reduction of 4-nitrophenol (4-NP) by sodium borohydride or H2. The kinetic data of 4-NP hydrogenation catalyzed by Pd/SAM-PDA are fitted to a Langmuir–Hinshelwood (L–H) model, and the calculated apparent activation energy of this process is 40.77 kJ mol–1.

Recent studies with better catalytic models show the structure sensitivity of noble-metals for catalytic hydrogenation. The size and shape of noble-metal nanocrystals have a great impact on their reaction performance in hydrogenation. Essentially, the exposed crystal planes, which primarily determine the morphology of a nanocrystal, tremendously affect its catalytic behavior. Therefore, many new methods involving controllable nucleation and growth processes have been developed to prepare uniform noble-metal nanocrystals with tunable sizes and shapes for catalytic hydrogenation. This paper presents a brief overview of the activity and selectivity of noble-metal nanocrystals with well-defined facets in the field of catalytic hydrogenation. High activity and controllable selectivity in hydrogenation have been achieved based on the shaped noble-metal nanocatalysts.

Water-dispersible magnetic Fe3O4 nanowires were synthesized at room temperature by the coprecipitation method using bio-inspired dopamine as a shape-directing surfactant. The as-synthesized nanowires were used to load a noble metal (Pd or Pt) for the preparation of magnetic nanocatalysts. The Fe3O4-nanowire supported noble metal exhibits bi-functional properties with stable water dispersion and excellent catalytic activity toward the hydrogenation of 4-nitrophenol and reduction of 4-nitrophenol by NaBH4 in water. In addition, the magnetic heterostructured nanocatalysts show good separation ability and reusability for at least 5 successive cycles. Moreover, Pd/Fe3O4 nanowires can also act as an efficient catalyst for the Suzuki reaction under aqueous conditions.

Aqueous-phase hydrogenation of 4-nitrophenol (4-NP) was investigated in the presence of free-standing or supported Pt nanoparticles (NPs) of various shapes. Uniform cubic and pseudo-tetrahedral Pt NPs with sub-10 nm sizes were obtained by the direction of bio-inspired small molecules, 3-hydroxybutyric acid (3-HB) and tropic acid (TA), respectively. The catalytic activity is found to be strongly affected by the nanoparticle shape and the support, SBA-15. Pseudo-tetrahedral Pt NPs directed by TA have superior activity to the cubic ones with 3-HB. But when loaded on SBA-15, cubic Pt(3-HB) NPs showed better performance than Pt(TA) NPs. Then the experimental data are fitted to a Langmuir–Hinshelwood (L–H) model involving a surface reaction controlling mechanism for 4-NP hydrogenation. This model follows a dual-site adsorption with molecular adsorption of 4-NP and dissociative adsorption of hydrogen. The results show that the reaction catalyzed by pseudo-tetrahedral Pt(TA) NPs has lower apparent activation energy than that by the cubic Pt(3-HB) NPs. But after loading these NPs onto SBA-15, the apparent activation energy of Pt(3-HB)@SBA-15 decreased while that of Pt(TA)@SBA-15 increased in comparison with their corresponding free-standing NPs.

Decomposition of methanol into hydrogen and carbon monoxide is a potential endothermic reaction for advanced fuel-cooled thermal management technology. In this paper, thermodynamic analyses of methanol decomposition under low pressure (0.1 MPa) and high pressure (4.0 MPa) were first conducted for a better fundamental understanding of methanol cooling. Furthermore, thermal and catalytic decomposition of methanol were studied in an electrically heated tube reactor under 4 MPa. Excellent heat absorption ability of this process indicates that methanol is a promising fuel for active cooling technology. Then, the cofeeding of kerosene fuel with methanol has been carried out to investigate effects of methanol on product distribution, heat sink, and coking in the fuel-cooled process. Results show that the presence of methanol promotes the total heat sink, increases ethylene yield, and dramatically reduces coke deposition by the production of hydrogen as a dilution agent.

In this work, we demonstrate a convenient, efficient, and environmentally benign strategy to achieving antimicrobial and antiadhesive purposes using a silver–zwitterion nanocomposite. The synthesis of the nanocomposite relies on loading zwitterionic polymer brushes with Ag+ precursor ions, followed by their in situ reduction to Ag nanoparticle by ultraviolet (UV) irradiation. Both poly(sulfobetaine methacrylate) (pSBMA) and poly(carboxybetaine methacrylate) (pCBMA) have been studied as matrices for the embedding of silver. Well-dispersed silver nanoparticles are embedded into pCBMA matrices. The obtained pCBMA–silver hybrid (CB-Ag) is capable of killing bacteria upon contact and releasing dead bacteria under wet conditions. Results suggest the feasibility of using this nanocomposite system as a robust and reliable antimicrobial and antiadhesive platform for the prevention of microbial colonization.

ITQ-2 zeolites were prepared by sequential alkali-swelling and ultrasonic-delamination of precursor MCM-22 and characterized by X-ray powder diffraction, scanning electron microscopy, nitrogen adsorption–desorption, ammonia temperature-programmed desorption and in-situ Fourier-transform infrared spectroscopy. The delamination induced a change in the morphology of ITQ-2 zeolites from aggregated thin platelets to scattered platelets, together with a significant increase in external specific surface area, which reached a plateau at the ultrasonic treatment time of 3 h. The catalytic cracking of n-dodecane over ITQ-2 zeolites was evaluated with ITQ-2 coated on the inside wall of a tubular reactor at 550 °C and 4 MPa. The sample obtained by ultrasonic treatment of 3 h (ITQ-2-3) gave the highest initial conversion of n-dodecane, whereas those of 5 h and 1 h gave the conversion even lower than MCM-22, which was in agreement with the trend of the ratio of strong Lewis acid to the total acid amount. Although the amount of cokes deposited on ITQ-2-3 was larger than that on MCM-22, the former deactivated slowly, suggesting that a large external specific surface area benefits the stability of zeolite coatings.The morphology, external specific surface area, acid site properties and catalytic cracking performance of ITQ-2 zeolite could be affected greatly by the degree of delamination. The zeolite catalyst obtained by ultrasonic treatment of 3 h (ITQ-2-3) gave the highest initial conversion of n-dodecane.Download full-size image

•Discovery of reaction-driven restructuring of silver nanoparticles in water.•TEM characterization and molecular simulation for the restructuring process.•Drastically increased activity of silver via optimized reconstruction.Metal nanoparticles (NPs) have been studied extensively as catalysts due to their high activity. However, the application of metallic nanostructures in catalytic reactions is hampered by their uncontrollable performance due to their reconstruction in reactive environments. Here, controllable restructuring of silver NPs in the reactive environment has been achieved to increase their activity. Surface restructuring of the as-synthesized silver NPs was monitored in situ by UV–vis spectra. Kinetic analysis, transmission electron microscopy (TEM), and molecular simulation were conducted to investigate the mechanism of this process. Results indicate that this reaction-driven restructuring leads to the formation of reactive high-index facets on silver NPs. In the reduction of 4-nitrophenol by sodium borohydride, silver NPs with extremely high catalytic activity (surface-area-normalized rate constant of 13.22 s−1 m−2 L) were obtained via accurately controlled surface restructuring of silver NPs obtained by UV irradiation.Download high-res image (76KB)Download full-size image

•SBA-15 supported Ni-Co alloy catalysts are developed by an ethylene-glycol method.•The performance of nickel catalyst is improved by SBA-15, Ni-Co alloy and CeO2.•Complete and stable steam reforming of C12 is pursued at 923 K and 12 ml/gCat h.•Good dispersion of metal on SBA-15 is responsible for the high performance.Various nickel catalysts have been developed to pursue complete and stable steam reforming of n-dodecane at 923 K under high liquid hourly space velocity (LHSV) of 12 ml/gCat h and H2O/C of 4. Confinement of Ni nanoparticles by SBA-15, alloying of nickel and cobalt, and promotion of Ni-silica interaction by CeO2 have been adopted to improve catalytic 09performance of nickel. Ni, Ni-Co and CeO2-promoted Ni-Co supported on SBA-15 were prepared via a facile ethylene-glycol-assisted route. Various techniques including XRD, nitrogen adsorption–desorption, H2-TPR, TEM and TG/DTG were employed to characterize the fresh and spent catalysts. Results show that Ni/Ni-Co/Ni-Co-CeO2 nanoparticles are highly dispersed on mesoporous SBA-15 due to ethylene-glycol facilitation. Metal-support interaction is promoted by the presence of cobalt and CeO2. Steam reforming of n-dodecane was carried out to evaluate their catalytic performances under atmospheric pressure in a fixed-bed tubular reactor. The performance of nickel catalyst has been improved steadily by the support of SBA-15, alloying of Ni-Co and promotion of CeO2. Great enhancements of catalytic activity and stability have been achieved by these three strategies via effective inhibitions of Ni sintering and coke deposition. The catalyst of 3Ni-3Co-6CeO2@SBA-15 exhibits the highest conversion of n-dodecane (100%) and the best stability (only 7.5% deactivation in 7 h).

Recent studies with better catalytic models show the structure sensitivity of noble-metals for catalytic hydrogenation. The size and shape of noble-metal nanocrystals have a great impact on their reaction performance in hydrogenation. Essentially, the exposed crystal planes, which primarily determine the morphology of a nanocrystal, tremendously affect its catalytic behavior. Therefore, many new methods involving controllable nucleation and growth processes have been developed to prepare uniform noble-metal nanocrystals with tunable sizes and shapes for catalytic hydrogenation. This paper presents a brief overview of the activity and selectivity of noble-metal nanocrystals with well-defined facets in the field of catalytic hydrogenation. High activity and controllable selectivity in hydrogenation have been achieved based on the shaped noble-metal nanocatalysts.

Water-dispersible magnetic Fe3O4 nanowires were synthesized at room temperature by the coprecipitation method using bio-inspired dopamine as a shape-directing surfactant. The as-synthesized nanowires were used to load a noble metal (Pd or Pt) for the preparation of magnetic nanocatalysts. The Fe3O4-nanowire supported noble metal exhibits bi-functional properties with stable water dispersion and excellent catalytic activity toward the hydrogenation of 4-nitrophenol and reduction of 4-nitrophenol by NaBH4 in water. In addition, the magnetic heterostructured nanocatalysts show good separation ability and reusability for at least 5 successive cycles. Moreover, Pd/Fe3O4 nanowires can also act as an efficient catalyst for the Suzuki reaction under aqueous conditions.

Aqueous-phase hydrogenation of 4-nitrophenol (4-NP) was investigated in the presence of free-standing or supported Pt nanoparticles (NPs) of various shapes. Uniform cubic and pseudo-tetrahedral Pt NPs with sub-10 nm sizes were obtained by the direction of bio-inspired small molecules, 3-hydroxybutyric acid (3-HB) and tropic acid (TA), respectively. The catalytic activity is found to be strongly affected by the nanoparticle shape and the support, SBA-15. Pseudo-tetrahedral Pt NPs directed by TA have superior activity to the cubic ones with 3-HB. But when loaded on SBA-15, cubic Pt(3-HB) NPs showed better performance than Pt(TA) NPs. Then the experimental data are fitted to a Langmuir–Hinshelwood (L–H) model involving a surface reaction controlling mechanism for 4-NP hydrogenation. This model follows a dual-site adsorption with molecular adsorption of 4-NP and dissociative adsorption of hydrogen. The results show that the reaction catalyzed by pseudo-tetrahedral Pt(TA) NPs has lower apparent activation energy than that by the cubic Pt(3-HB) NPs. But after loading these NPs onto SBA-15, the apparent activation energy of Pt(3-HB)@SBA-15 decreased while that of Pt(TA)@SBA-15 increased in comparison with their corresponding free-standing NPs.