A dramatic morphology evolution from cobalt nanoparticles to one-dimensional cobalt nanochains have been found by the introduction of CO in the synthesis process. The competitive adsorption between oleylamine (OAm) and CO molecules on cobalt surface was analyzed by DFT calculations. The competitive adsorption provides an effective way to regulate the surface properties of cobalt nanoaparticles, thus adjusting the interactions between cobalt nanoparticles and leading the self-assembly formation of cobalt nanochains. The novel one-dimensional cobalt nanochains show superior activity for CO hydrogenation, thus providing a powerful strategy for the surface and morphology controlled synthesis of catalyst nanomaterials assisted by small molecules.

Bimetallic phosphides have attracted research interest for their synergistic effect and superior electrocatalytic activities for electrocatalytic water splitting. Herein, a MOF-derived phosphorization approach was developed to produce Ni2P–CoP bimetallic phosphides as bifunctional electrocatalysts for both hydrogen and oxygen evolution reactions (HER and OER). Ni2P–CoP shows superior electrocatalytic activities to both pure Ni2P and CoP toward HER and OER, revealing a strong synergistic effect. High-resolution transmission electron microscopy and energy dispersive X-ray spectroscopy elemental mapping analysis show that, in the sample Ni2P–CoP, the Ni2P and CoP nanoparticles with an average particle size 10–20 nm were mixed closely on the nanoscale, creating numerous Ni2P/CoP interfaces. By comparison with the sample Ni2P+CoP, in which seldom Ni2P/CoP interfaces exist, we documented that the Ni2P/CoP interface is an essential prerequisite to realize the synergistic effect and to achieve the enhanced electrocatalytic activities in Ni2P–CoP bimetallic phosphides. This finding is meaningful for designing and developing bicomponent and even multicomponent electrocatalysts.Keywords: bimetallic phosphides; electrocatalysis; interfaces; synergistic effect; water splitting;

For a surfactant−inorganic−water system, we study systemically the epitaxy process of the surfactant-templated inorganic nanomaterial on a patterned surface with a lattice Monte Carlo method. It is found that by using ring-patterned substrate as a template, vertically oriented inorganic material may be formed through the nanometer-scale epitaxy. For all the cases studied in this work, a hemicylinder initially formed on the ring pattern behaves as nucleation sites for the following growth process. Different parameters, such as surfactant architecture, bulk surfactant concentration, fraction of inorganic component, and pattern size, are found to affect the epitaxial growth process of the inorganic nanomaterial. The change of surfactant architecture alters the structure of formed aggregates significantly, thus affecting the epitaxial growth. For the effects of surfactant concentration, it is found that there exists a critical value. If and only if the bulk surfactant concentration is higher than the critical value is the epitaxial growth of inorganic material nucleated from the patterned substrate possible. For the effects of the fraction of the inorganic component, simulation results indicate that there also exists a volume fraction above which the nanomaterial growth is dominated by macrophase separation but not templated by the substrate pattern. The geometry of the chemical modification of the surface also shows significant effects on the nanometer-scale epitaxy, depending on whether its sizes are commensurate with the morphology of the formed inorganic nanomaterials or not.

One-dimensional Ag–Ni core–shell nanowires were successfully synthesized by a simple two-step method, in which Ni shells grow epitaxially at the surface of silver nanowires (Ag NWs) to form a unique core–shell structure. The thickness of Ni shells can be finely controlled from 50 to 150 nm by adjusting the initial Ni to Ag atomic ratios. The electrocatalytic performance of the Ag–Ni core–shell NWs can be adjusted by tuning their compositions, and the optimized Ag to Ni atomic ratio is 1 : 1. The Ag–Ni core–shell nanowires exhibit superior electrocatalytic activity to pure Ni nanoparticles and Ag NWs, showing a strong synergistic effect toward alkaline hydrogen evolution reaction (HER). A morphological effect was demonstrated by comparing with Ag–Ni core–shell nanoparticles. The enhanced HER activity of Ag–Ni core–shell NWs can be attributed to the synergetic effect between Ag and Ni, the larger number of surface active sites and the fast charge transport. This approach provides a reasonable attempt for designing and developing 1D electrocatalysts based on Ag nanowires.

In this review we focus on the catalytic removal of a series of N-containing exhaust gases with various valences, including nitriles (HCN, CH3CN, and C2H3CN), ammonia (NH3), nitrous oxide (N2O), and nitric oxides (NOx), which can cause some serious environmental problems, such as acid rain, haze weather, global warming, and even death. The zeolite catalysts with high internal surface areas, uniform pore systems, considerable ion-exchange capabilities, and satisfactory thermal stabilities are herein addressed for the corresponding depollution processes. The sources and toxicities of these pollutants are introduced. The important physicochemical properties of zeolite catalysts, including shape selectivity, surface area, acidity, and redox ability, are described in detail. The catalytic combustion of nitriles and ammonia, the direct catalytic decomposition of N2O, and the selective catalytic reduction and direct catalytic decomposition of NO are systematically discussed, involving the catalytic behaviors as well as mechanism studies based on spectroscopic and kinetic approaches and molecular simulations. Finally, concluding remarks and perspectives are given. In the present work, emphasis is placed on the structure–performance relationship with an aim to design an ideal zeolite-based catalyst for the effective elimination of harmful N-containing compounds.

Mesoporous LaFeO3 having extremely high surface area was prepared by means of one-step infiltration hard-template (HT) nanocasting method using SBA-15 as a template, which could be partially leached out by NaOH solution. Although this lanthanum ferrite is not an exact replica of the corresponding HT, its specific surface area could reach 158 m2 g−1, which is much higher than that of the sample prepared by a traditional sol–gel method (19 m2 g−1). Subsequently, LaFeO3/SBA-15 hybrid samples containing the different amounts of Si residue were obtained by carefully controlling the leaching time under 2 M NaOH. These as-prepared samples were characterized by XRD, TEM, XPS, XRF, H2-TPR, N2 physisorption techniques, NH3-TPD, CH3Cl-TPD, as well as in situ NH3 DRIFTS, which were further evaluated for the catalytic combustion of methyl chloride (CH3Cl). Thereafter, the effect of silica residues of HT on the texture, morphology, acidity/basicity, and the catalytic activities of the prepared nanocasted samples was systematically studied. The more silica HT was left in samples, the lower surface area associated with the less adsorbed oxygen and the worse catalytic activity was achieved. The acidity of the prepared LaFeO3 samples decreased along with reduction in the residual Si content; however, the opposite occurred for the related basicity which was found to play an important role on CH3Cl catalytic oxidation. The total collapse of mesoporous structure and the generation of some new crystal phases were observed simultaneously with an obvious drop in its BET surface area (down to 69 m2 g−1), as the sample was treated by a highly concentrated NaOH (10 M) in order to entirely remove HT silica.

In order to investigate the activities of perovskite-type mixed oxides for selective catalytic reduction (SCR) of NO with NH3, a series of LaBO3 or La2BO4 perovskite-based catalysts with different B-site ions (B = Cu, Co, Mn, and Fe) was prepared by citrate complexation procedure and characterized by XRD, BET, TPD of NO + O2 and NH3. It was found that Mn-based perovskite exhibited the best catalytic activity, yielding 78% NO conversion at 250 °C. The NH3 adsorption ability of the perovskites is the key factor for the SCR performance. In situ DRIFTS investigation was further carried out over LaMnO3 to explore the reaction mechanism. It is revealed that the SCR reaction starts with NH3 chemical adsorption, being thought as the rate-determining step. The mechanism essentially involves a Langmuir–Hinshelwood mechanism mainly depending on an interaction between NH4+ ionic species and nitrite species in the low-temperature range.Graphical abstractHighlights► LaMnO3 achieved an ideal performance for low-temperature NO-SCR by NH3. ► The ability of perovskites for NH3 adsorption plays a ruling role on NO reduction. ► The SCR reaction follows L–H mechanism involving nitrite and NH4+ species.

This work tried to identify the relationship between the internals of selective catalytic reduction (SCR) system and mixing performance for controlling ammonia (NH3) slip. In the SCR flow section, arranging the flow-guided internals can improve the uniformity of velocity distribution but is unfavorable for the uniformity of NH3 concentration distribution. The ammonia injection grids (AIG) with four kinds of nozzle diameters (i.e., 1.0 mm, 1.5 mm, 2.0 mm, and mixed diameters) were investigated, and it was found that the AIG with mixed nozzle diameters in which A3, A4, B3, and B4 nozzles’ diameters are 1.0 mm and other nozzles’ diameters are 1.5 mm is the most favorable for the uniformity of NH3 concentration distribution. In the SCR reactor section, the appropriate space length between two catalyst layers, which serves as gas mixing in order to prevent maldistribution of gas concentrations into the second catalyst layer, under the investigated conditions is about 100, 1000, and 12 mm for honeycomb-like cordierite catalyst, plate-type catalysts with parallel channel arrangement, and with cross channel arrangement, respectively. Therefore, the cross channel arrangement is superior to the parallel channel arrangement in saving the SCR reactor volume.

This paper reports a comparative study of a series of La1−x(M)xCoO3 (M = Ce and Sr) perovskites and the related M′Ox (M′ = La, Co, Ce, and Sr) sample oxides. These catalysts were characterized by N2 adsorption, X-ray diffraction (XRD), temperature-programmed desorption (TPD) of oxygen, temperature-programmed reduction (TPR) by hydrogen, and temperature-programmed combustion (TPC) of soot. In the presence of perovskite-type catalysts, the soot oxidation was promoted, showing a shift of CO2 peaks toward lower temperature compared to the non-catalytic process. In addition, the catalytic activity of these perovskites was found to follow the trend La0.8Ce0.2CoO3 > La0.9Ce0.1CoO3 > La0.9Sr0.1CoO3 > La0.8Sr0.2CoO3 ≈ LaCoO3. A mechanism was proposed with an attack of soot by surface oxygen species, which migrate from the perovskite surface. The generation of CO (or carbonyl groups) as an intermediate and the possible formation of carbonate species over the most basic compounds are also discussed.

For producing pure hydrogen from biomass gasification with steam as the gasifying agent, an intensified process is proposed. In the process, a bubbling fluidized bed gasifier is used for the steam gasification of biomass, a steam reformer is used for upgrading the biosyngas, and an H2-membrane water-gas-shift (HMWGS) reactor is used for converting the carbon monoxide and separating the hydrogen. Pure hydrogen is the product of the process. High-purity CO2 can be produced and taken as a coproduct. To better simulate the proposed process, models for the steam-blown fluidized bed gasifier and catalytic steam reformer have been developed. The simulation results have been compared with the experimental data, and good agreement has been obtained. The analysis of the proposed process is carried out in terms of the amount of pure hydrogen per kilogram of biomass and the overall thermodynamic efficiency of the process. Factors affecting the pure hydrogen production and thermodynamic efficiency have been studied and discussed.

For a surfactant−inorganic−water system, we study systemically the epitaxy process of the surfactant-templated inorganic nanomaterial on a patterned surface with a lattice Monte Carlo method. It is found that by using ring-patterned substrate as a template, vertically oriented inorganic material may be formed through the nanometer-scale epitaxy. For all the cases studied in this work, a hemicylinder initially formed on the ring pattern behaves as nucleation sites for the following growth process. Different parameters, such as surfactant architecture, bulk surfactant concentration, fraction of inorganic component, and pattern size, are found to affect the epitaxial growth process of the inorganic nanomaterial. The change of surfactant architecture alters the structure of formed aggregates significantly, thus affecting the epitaxial growth. For the effects of surfactant concentration, it is found that there exists a critical value. If and only if the bulk surfactant concentration is higher than the critical value is the epitaxial growth of inorganic material nucleated from the patterned substrate possible. For the effects of the fraction of the inorganic component, simulation results indicate that there also exists a volume fraction above which the nanomaterial growth is dominated by macrophase separation but not templated by the substrate pattern. The geometry of the chemical modification of the surface also shows significant effects on the nanometer-scale epitaxy, depending on whether its sizes are commensurate with the morphology of the formed inorganic nanomaterials or not.

The effect of various gases (O2, hydrocarbons, CO, H2, NOx, SO2, and H2O vapor) presenting in the diesel exhaust on soot combustion using LaCoO3 as a catalytic material was investigated in this paper. A significant promotion of the combustion rate was found following a trend of 10% H2O addition > 3,000 ppm NOx > 1% H2 or 3,000 ppm C3H6 addition, while the improvement in soot oxidation due to the introduction of 3,000 ppm CO or 3,000 ppm CH4 into the reactant gas is relatively less. The wet pretreatment of LaCoO3 with 10% steam before soot oxidation hardly affects the combustion behavior. Interestingly, 10% water vapor in the reaction feed produced a significant promoting effect on combustion. In contrast, 30 ppm SO2 treating led to an obvious deactivation likely owing to the coverage of active sites by sulfate compounds.

Grand canonical Monte Carlo (GCMC) simulations and configurational-bias Monte Carlo simulations (CBMC) have been performed to compute and compare the pure component adsorption isotherms of C1–C7 linear alkanes in MFI, BEA, and MOR zeolites at 300 K. It is demonstrated that generally, the surfaces of the three zeolites available for adsorption are not energetically homogeneous; adsorption of the alkanes in the three zeolites can be divided into two steps, in the first step of which molecules are adsorbed in the strong sites and on the later of which on the weak sites; all isotherms obtained can be well described by the dual-site Langmuir equation, though the saturation loadings and the adsorption strengths are different for the three different topologic zeolites. A quantitative analysis of the isotherms shows that the Henry’s law constants in the three zeolites obey a similar linear relation to the number of carbon atoms of the alkanes.

The condensation of silicic acid with aluminate in alkaline environment, the essential reaction of zeolite synthesis, is studied using the density functional theory, with the hybrid functional B3LYP in conjunction with the 6-311++G(d, p) basis set. The Si(OH)4 monomer and Al(OH)4− anion are used as the reactant models to study the condensation pathway in basic solution. The solvent effect is included by the COSMO-RS model. The study includes the complete geometry optimization and frequency calculation of reactants, products, reaction intermediates, and transition states, as well as the calculation of the activation energy of the different pathways involved. The intrinsic reaction coordinate method is used to verify the reactant and product corresponding to the transition state. The calculation shows that the formation of Si–O–Al linkage can proceed via two possible reaction pathways. The first is a single-step process, in which the formation of SiO···Al bond and removal of water are synchronous, with the activation energy of 83.7 kJ/mol. The second is a stepwise route, in which the AlO···Si bond is first formed to give a 5-coordianted Si intermediate, and then water is removed to yield a dimer aluminosilicate, with the barriers of 62.7 and 69.3 kJ/mol for the two steps, respectively. Theoretical study of formation mechanism of aluminosilicate in the synthesis of zeolites

The double-bond isomerization of 1-pentene to cis-2-pentene on the surface of the molecular sieves has been investigated by using density functional theory with a cluster model simulating the zeolite materials. The microcosmic interaction of the pentene molecule with the Brønsted acid site of the zeolite leads to the formation of a π-complex, where the CC double bond is weakly coordinated to the proton of the Brønsted acid site. The transition state has an eight-member cyclic structure, in which two hydrogen atoms are situated between one oxygen atom of the zeolite and one carbon atom of the migrating double bond, respectively. The calculations of the intrinsic reaction coordinate indicate that the double-bond isomerization of 1-pentene proceeds via a concerted proton transfer between the Brønsted acid sites of the zeolite and the pentene molecules. The calculated activation energy of 11.74 kcal/mol is close to the experimental data.

A study of the aggregation of silica sol particles is presented by using a Monte Carlo simulation including the reaction parameters: activation energy, temperature, and particle concentration. In this simulation, all of the system particles are classified as active and inactive types; only the activated particles can aggregate into clusters, and consequently the aggregation exhibits selectivity. The influences of the above reaction parameters on structural properties and growth kinetics of aggregates are investigated and compared with the existing relevant results. The evolutions of the fractal dimension and size distribution of aggregates over the entire process suggest that the sol system exhibits the behaviors of diffusion-limited cluster aggregation at earlier times and crosses over to those of diffusion-limited aggregation at later times.

Catalytic activities of M (Fe, Cu, Co)–beta (BEA) zeolites for N2O direct decomposition were systematically investigated by employing both experimental and theoretical [density functional theory (DFT)] approaches. The activities of M–BEA determined by intrinsic kinetic evaluations are in good agreement with the DFT calculations and the microkinetic analyses, revealing that the distinguishing activities of M–BEA were mainly attributed to their distinct energy barriers for the O2 desorption (Part 3). During the DFT calculations, a unique intermediate (IM) was generated only over Co–BEA, which was verified by the activity evaluation and N2O-TPD experiments, showing that the formation of IM reduced N2O decomposition rate of Co–BEA. The negative effect of the IM was thereafter investigated by the microkinetic analyses through which it was known that the second forward reaction rate constant of Co–BEA was lower than its reverse reaction rate constant, resulting in a final decline of the N2O decomposition rate.Graphical abstractCatalytic performances of M (Fe, Cu, Co) -BEA zeolites for N2O direct decomposition were comparatively investigated revealing that the distinguishing activities of M–BEA were mainly attributed to their distinct energy barriers for the O2 desorption resulting in an activity sequence Co–BEA > Fe–BEA > Cu–BEA. The transition metal ions serving as the active sites for N2O decomposition were confirmed to be the main species existing on the M–BEA. A unique intermediate (IM) was generated only over Co–BEA, which could slow down the N2O decomposition. This negative effect of the IM was thereafter investigated by the microkinetic analysis through which it was known that the second forward reaction rate constant of Co–BEA was lower than its reverse reaction rate constant, leading to a final decline of the N2O decomposition rate.Download high-res image (193KB)Download full-size imageHighlights► N2O direct decomposition mechanisms over M–BEA (M = Fe, Co, Cu) were comparatively investigated. ► Activity differences of M–BEA were due to the distinct energy barriers of O2 desorption. ► An intermediate was merely generated over Co–BEA reducing its N2O decomposition rate. ► Microkinetic analyses quantitatively explained the activity differences of M–BEA.

An integrated process has been proposed for the production of ultrapure hydrogen from biomass gasification with air. The process consists of an air-blown bubbling fluidized bed gasifier, a steam reformer, and a water-gas-shift membrane reactor. A non-isothermal model has been developed to simulate the fluidized bed gasifier, and a one-dimensional model has also been developed to simulate the steam reformer. The simulation results are compared with the experimental data, and good agreement is obtained. Based on the simulation results, the thermodynamic analysis of the integrated process is carried out. The simulation and analysis provide a quantitative tool for gaining insight into the process.

A series of mono-functional M/SBA-15 (M = Cu, Fe, Cr, and Al) and bifunctional M′/SBA-15 (M′ = Cu–Al, Fe–Al, and Cr–Al) catalysts was prepared via an incipient wetness impregnation, and further characterized by N2 adsorption, XRD, TEM, H2-TPR, Al27-NMR, and XPS as well as activity test for C3H6 + NO + O2 reaction. Ordered mesoporous structure of SBA-15 was well maintained even after impregnating the various metallic components. The deNOx activities of investigated catalysts follow a trend of Cu–Al/SBA-15 > Cu/SBA-15, Fe/SBA-15 > Cr–Al/SBA-15 > Cr/SBA-15 ≫ Fe–Al/SBA-15, Al/SBA-15 > SBA-15. Synergistic effect between copper and alumina was achieved showing a satisfactory NO conversion of approximately 80% over Cu–Al/SBA-15 at temperature as low as 350 °C under an atmosphere of 3000 ppm NO, 3000 ppm C3H6, 1% O2 and GHSV of 60,000 h−1. The SCR performance was found to be strongly correlated to the redox properties of tested catalysts, essentially chemical nature of supported metals, and surface density of active metallic species.Graphical abstractDownload high-res image (297KB)Download full-size imageHighlights► Copper or aluminum loading effectively enhances the NO conversion for bare SBA-15. ► Al presence is beneficial for suppressing the formation of CuO cluster and promoting the redox properties of Cu2+ species. ► Al nuclei have been mainly incorporated into the SBA-15 framework with the assistance of copper loading. ► A synergetic effect is achieved between copper and aluminum, resulting in an optimal performance over Cu–Al/SBA-15 showing NO conversion of ∼88% at 400 °C.

The effect of adding aromatic compounds and varying the AlCl3 molar fraction on the catalytic performance of chloroaluminate ionic liquids in isobutane/2-butene alkylation was investigated. 27Al NMR results and comparison with alkylation catalyzed by solid AlCl3 reveal that the activity of the ionic liquids presumably comes from traces of AlCl3 or Al2Cl6. The addition of benzene increases the selectivity of C8 as well as the TMP:DMH ratio in the alkylate. The performance of the modified catalyst is optimized at high isobutane to 2-butene ratios and low temperatures. The used catalyst can be regenerated by replenishment of the aromatic additives.

Mesoporous LaFeO3 having extremely high surface area was prepared by means of one-step infiltration hard-template (HT) nanocasting method using SBA-15 as a template, which could be partially leached out by NaOH solution. Although this lanthanum ferrite is not an exact replica of the corresponding HT, its specific surface area could reach 158 m2 g−1, which is much higher than that of the sample prepared by a traditional sol–gel method (19 m2 g−1). Subsequently, LaFeO3/SBA-15 hybrid samples containing the different amounts of Si residue were obtained by carefully controlling the leaching time under 2 M NaOH. These as-prepared samples were characterized by XRD, TEM, XPS, XRF, H2-TPR, N2 physisorption techniques, NH3-TPD, CH3Cl-TPD, as well as in situ NH3 DRIFTS, which were further evaluated for the catalytic combustion of methyl chloride (CH3Cl). Thereafter, the effect of silica residues of HT on the texture, morphology, acidity/basicity, and the catalytic activities of the prepared nanocasted samples was systematically studied. The more silica HT was left in samples, the lower surface area associated with the less adsorbed oxygen and the worse catalytic activity was achieved. The acidity of the prepared LaFeO3 samples decreased along with reduction in the residual Si content; however, the opposite occurred for the related basicity which was found to play an important role on CH3Cl catalytic oxidation. The total collapse of mesoporous structure and the generation of some new crystal phases were observed simultaneously with an obvious drop in its BET surface area (down to 69 m2 g−1), as the sample was treated by a highly concentrated NaOH (10 M) in order to entirely remove HT silica.