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Waste tire was heat-treated to prepare sulfur self-doped chars via pyrolysis and activation processes. Pyrolytic waste tire chars were activated at different temperatures (600 °C, 800 °C, 1000 °C, and 1200 °C) with K2FeO4 additive ratios (mass ratio of K2FeO4 to char) being 0.5, 1, 2, and 3, respectively. The effective activation occurred over 600 °C with K2FeO4 additive ratios over 0.5. The strongest activation occurred at 1000 °C with K2FeO4 additive ratio of 3, and the specific capacitance increased to 129.5 F/g at 1 A/g, which was six times higher than that without K2FeO4. The activation mechanism revealed that higher K2FeO4 additive ratio promoted the transformation of large aromatic ring systems (≥6 rings) to small ones and smaller pores formation. When K2FeO4 additive ratio was less than 2, high ratio not only promoted alkyl-aryl C-C bonds formation, but also inhibited sulfur enrichment with S 2p3/2 (sulphide bridge) converting to S 2p5/2 (sulphone bridge). But when the ratio was further increased, slight decomposition of alkyl-aryl C-C bonds with the promoted conversion of S 2p5/2 to S 2p3/2 was witnessed. Furthermore, higher activation temperature promoted the conversion of aromatic ring systems and alkyl-aryl C-C bonds to form ordered graphitic structures. S 2p3/2 was enriched before 800 °C, but both S 2p3/2 and S 2p5/2 were released at higher temperature. Formation of smaller pores was promoted before 1000 °C, but the char structure was then destroyed to form larger pores when temperature was further increased.

The evolutions of different types of coke deposition, including amorphous carbon, carbon networks (CNWs) and carbon nanotubes (CNTs), were clarified on Ni-based catalyst during catalytic cracking and reforming of biomass tar. Different from the changing of total coke, the amount of amorphous carbon gradually increased at the decreasing rate, while the amount of graphite carbon (CNWs and CNTs) firstly increased and then decreased after 60min reactions. The formation of amorphous carbon was prior to that of graphite carbon, and it was proved that a part of amorphous carbon converted to graphite carbon. After the 60min reaction, the proportion of graphite carbon and graphitization degree of coke decreased. The graphite carbon underwent the aging process in which the graphite structure would be destroyed to amorphous carbon. In cracking reaction, CNWs was the main type of graphite carbon which encapsulated the Ni particles with graphitic layers. After the addition of steam, the toluene conversion and coke amount remarkably increased in reforming reaction. Plenty of CNTs grew on the surface of catalysts and the amount of CNTs reached the maximum of about 200mg/g-cata at 60min. These research results are important for understanding the formation mechanism of coke and optimization the produced CNTs.

A robust monolith catalyst has been fabricated involving the combination of nanodiamonds (NDs) and mesoporous carbon modified by nitrogen and phosphorus (ND@NMC-xP, x = amount of ammonium biphosphate) on a β-SiC foam. The ND@NMC-0.02 P/SiC monolith catalyst with 0.2 at.% of P elements exhibits an excellent catalytic performance for oxidative dehydrogenation of ethylbenzene (EB), delivering 90.2% selectivity to styrene (ST) up to 32.6% conversion. The specific conversion rate of monolith catalyst based on the unit weight of NDs and mesoporous carbons (25.3 mmol gact. phase−1 h−1) is 3-fold higher than that of unsupported NDs. The role of nitrogen is believed to enhance the density of active sites and thus offering a high EB conversion, whereas the addition of phosphorus inhibits deep oxidation of EB to carbon oxides and therefore for a high selectivity to ST. The monolith catalyst not only contributes a high utilization efficiency of NDs but also mitigates the high pressure drop across the catalytic bed, which is potentially suitable for a real industrial process.

The char samples were prepared from the coal impregnated with NaCl under different steam concentrations and temperatures. The mode of occurrence of sodium and the contents of sodium in different chars with the same conversion ratio were analyzed by inductively coupled plasma mass spectrometry. The effects of steam and temperature on the migration and transformation of sodium in the coal during the thermal conversion processes were studied. The results showed that the increase of steam concentration enhanced the release of water-soluble sodium during the thermal conversion of coal and promoted the transformation of water-soluble sodium into ammonium acetate, hydrochloric acid and insoluble sodium. As a result, the release of sodium was suppressed to a certain extent. It was also observed that increasing the reaction temperature could promote the release of water-soluble sodium and promote the transformation of water-soluble sodium to the other soluble forms of sodium. The evolution of char structure was an important influence on the release of sodium. The results revealed that the degrees of char condensation increased with the steam gasification reaction. The formation of large aromatic ring structures from the condensation of the small aromatic rings played the important role in the encapsulation of sodium, which would inhibit the release of sodium.

Electronic properties of monolayer tellurium (Te) with three proposed atomic configurations under external electric field were investigated through first-principles calculations. The calculated results demonstrate that α-Te and γ-Te have indirect band gaps, whereas β-Te, when no electric field is applied, can be considered as a direct semiconductor. An interesting structural change occurs in α- and γ-phase Te under a specific electric field strength, as does a change in structural chirality. In the presence of a perpendicular electric field, the band gaps can be modified and drawn close to 0 eV at a certain critical electric field strength. Before that, the band gaps of α-Te and γ-Te are nearly constant, while that of β-Te shows a quadratic relationship to electric field strength. These findings not only enrich our understanding of the electronic properties of monolayer tellurium but also show that monolayer tellurium has tremendous potential in nanoscale electronic devices owing to its tunable band gaps.

Pyruvic acid and pyruvate derivatives are important chemical intermediates which are normally produced using metal-based catalytic materials that could cause serious environmental problems. In the present work, renewable nanocarbon catalysts are applied in this system, and a solvent free and highly selective oxidative dehydrogenation of ethyl lactate (EL) process is achieved to produce ethyl pyruvate (EP) under mild reaction conditions. Chemical titration results provide direct evidence that ketonic carbonyl groups on nanocarbon are active sites for this reaction. Raman, XPS and model catalyst experimental results have shown that there is a dynamic transformation between defects and oxygen functionalities during the catalytic reactions. The reaction pathway is revealed via kinetic analysis, which may shed light on the rational design of carbon catalysts and their potential catalytic applications in the field of fine chemical productions.

The formation of highly graphitic phenolic resin chars (GPFCs) during catalytic carbonization at relatively low reaction temperature (1200-1600 °C) using novel Ni-Zn-B alloy catalyst with small amount of addition (5-15%) was systematically studied. Only two kinds of graphites (turbostratic graphite and ordered graphite) can be found in GPFCs after catalytic carbonization with Ni-Zn-B and their proportions were changed with reaction conditions. When Ni-Zn-B was involved at 1200-1600 °C, the phenolic resin char was fully transformed to be graphite, and ordered graphite content increased to 28.42% at 1400 °C, which was also almost twice of ordered graphite content in the char catalyzed by pure Ni. But the order graphite content would decrease due to sintering at higher reaction temperature. The addition of Zn and B can promote nickel-based alloy catalytic action by reducing melt point and accelerating graphitization respectively. It was also found that ordered graphite content could be used as a key evaluation parameter to directly reflect the quality of GPFCs based on detailed characteristics analysis. The model between three reaction conditions (reaction temperature, retention time, catalyst content) and ordered graphite content was built with artificial neural network (ANN), and the prediction accuracy of ANN was high up to 91.48%.

Density functional theory (DFT) calculations have been employed to systematically investigate the strain-modulated electronic properties of monolayer tellurium. The results demonstrate that at zero strain γ-phase monolayer tellurium is found to be more energetically favorable than either the α-phase or β-phase which were fabricated through molecular-beam epitaxy. All studied phases are found to exhibit semiconductor characteristics, of which α- and γ-phases possess indirect band gaps whereas β phase is a direct band gap semiconductor. It is also found that the resulting band gap values approach zero at a large strain regime for all systems and the effective mass of electron and hole can be effectively modified by biaxial strain as well. These findings extend the knowledge on two-dimensional tellurium and provide potential applications in electronic devices.

We report a nanocarbon material with nanodiamond (ND) core and graphene shell (ND@G) as a support for Pd nanocatalysts. The designed catalyst performed good selectivity of styrene (85.2%) at full conversion of phenylacetylene and superior stability under mild conditions. Supported Pd catalysts are characterized by means of high resolution transmission electron microscopy (HRTEM), Raman, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and H2 temperature-programmed reduction (H2-TPR). The results clearly show that formation of the strong metal-support interaction (SMSI) between Pd nanoclusters and the defective graphene shell helpfully modifies the selectivity and stability of the Pd-based catalysts.

The post-Claus selective catalytic oxidation of H2S reaction in a continuous mode is demonstrated on N-doped 3D mesoporous carbon/carbon nanotube (N-C/CNT) monoliths at a reaction temperature highe...

A metal-free catalytic system combining oxidized carbon nanotubes (oCNTs) and ionic liquids (ILs) is presented for the oxidation of aromatic thiophene compounds with H2O2 as an oxidant. The oCNTs exhibit impressively high activity and stability in the system, which show an even better performance than those of some reported metal catalysts. The ILs are proved to have indispensable influence on the enhanced catalytic performance of the oCNTs. Detailed characterization by TG-MS and XPS demonstrates that the carbonyl groups are the active sites for the oxidation process, which is further supported by the deactivation and the model catalysts experiments. The quantitative analysis of different oxygen groups in oCNTs could be achieved by an isothermal temperature programmed TG-MS method. The concentration of carbonyl groups is 1.46 mmol per 1 g oCNTs and the turnover frequency of oCNTs could also be obtained (10.7 h−1 in the presence of OmimPF6). H2O2 decomposition experiments combined with the EPR results reveal that the presence of OmimPF6 can avoid the intermediate HO• to form O2 and then improve the catalytic performance of oCNTs for the oxidation of dibenzothiophene.

To understand the potential leaching toxicity of V in spent SCR catalysts for human and environment, the leaching behavior of V in spent V2O5-WO3/TiO2 SCR catalysts before and after cement stabilization/solidification (S/S) process was investigated. The results showed that the cement mixing ratio, curing time and solidifying agents (Na2S and sodium diethyl dithiocarbamate (DDTCNa)) obviously affect the leaching ability of V in spent SCR catalysts. The leaching amount, leaching concentration and leaching rate of V in original spent SCR catalyst are 137.98 mg/kg, 13.79 mg/L and 1.82%, respectively. After the spent SCR catalyst was solidified with cement and cured for 28 days, the leaching concentrations of V in catalyst-cement solidified waste are 2.27 mg/L for 30% of cement addition and 0.14 mg/L for 70% of cement addition, respectively. Increasing cement mixing ratio and curing time could decrease the leaching concentrations of V in the cement solidified waste by affecting the generation of V5+-bearing species, which was identified by XRD, BET, SEM and FTIR. The heavy metal V could be immobilized through the formation of VO43--bearing compounds in hydrating cement matrix. Evaluation on the leaching concentrations of V after adding Na2S and DDTCNa in cement solidified waste revealed that Na2S and DDTCNa are capable of reducing leaching concentrations of V from 6.25 mg/L to 5.74 mg/L and 4.65 mg/L, respectively. DDTCNa showed a better solidification performance for V compared to Na2S.

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.

A carbon supported carbon nitride is reported here as a catalyst for the direct conversion of acetylene and 1,2-dichloroethane (EDC) to vinyl chloride monomer (VCM). We demonstrate that increasing ...

The interface at the metal oxide-carbon hybrid heterojunction is the source to the well-known "synergistic effect" in catalysis. Understanding the structure-function properties is key for designing more advanced catalyst-support systems. Using a model MnIII-O x single-layer catalyst on carbon, we herein report a full elucidation to the catalytic synergism at the hybrid heterojunction in the oxygen reduction reaction (ORR). The successful fabrication of the single-layer catalyst from bottom-up is fully characterized by the X-ray absorption fine structure and high-resolution transmission electron microscopy. For oxygen electrocatalysis over this model hybrid heterostructure, our results, from both theory and experiment, show that the synergistic ORR truly undergoes a cooperated two-step electrocatalysis with catalytic promotion (Δ Eonset = 60 mV) near the heterojunction and over the single-layer catalyst through an interfacial electronic interplay, rather than an abstruse transition towards a one-step dissociative pathway. Finally, we report a superior peroxide-reducing activity of 432.5 mA cm-2 mg(M)-1 over the MnIII-O x single-layer.

Though photoluminescence (PL) of Si quantum dots (QDs) has been known for decades and both theoretical and experimental studies have been extensive, their luminescence mechanism has not been elaborated. Several models have been proposed to explain the mechanism. A deep insight into the origin of light emissions in Si QDs is necessary. This work calculated the ground- and excited state properties of hydrogenated Si QDs with various diameters, including full hydrogen passivation, single Si[double bond, length as m-dash]O ligands, single epoxide and coexisting Si[double bond, length as m-dash]O and epoxide structures in order to investigate the dominant contribution states for luminescence. The results revealed that even a single oxygen atom in hydrogenated Si QDs can dramatically change their electronic and optical properties. Intriguingly, we found that a size-independent emission, the strongest among all possible emissions, was induced by the single Si[double bond, length as m-dash]O passivated Si-QDs. In non-oxidized Si-QDs exhibiting a core-related size-tunable emission, the luminescence properties can be modulated by the ligands of Si QDs, and a very small number of oxygen ligands can strongly influence the luminescence of nanocrystalline silicon. Our findings deepen the understanding of the PL mechanism of Si QDs and can further promote the development of silicon-based optoelectronic devices.

Char-bound nitrogen [char(N)] is confirmed to be the real intermediate in heterogeneous reduction during coal combustion. Aiming to have a deep insight into the interaction mechanism between NO and char(N) containing different functional forms of nitrogen, a comprehensive theoretical exploration with density functional theory at M06–2X/6–31G(d,p)//def-TZVP level is performed. The detailed electronic descriptions of char(N) surface based on spin density, Mulliken atomic charge and electrostatic potential exhibit the attack sites and electron donating capability during NO chemisorption in the following order: char(N-5) N bond and promote N2 separation. The migration of oxygen atoms to adjacent active sites is thermodynamically conducive to reduction reactions, leading to the preferred pathway of N2 release on char(N-5) and char(N-X) surfaces. Contiguous active sites remaining along char edge are unfavorable for N2O detaching, while beneficial to NO further chemisorption for consecutive reactions, resulting in the great contributions of char(N-5) in reducing NO. The lower energy barriers for NO reduction follow the sequence coincident with the results of electronic property analysis. The kinetically favorable temperatures and activation energies of different char(N) for reducing NO are determined, which is consistent with previous experiments. The theoretical results provide evidences to explain microscopic mechanism of NO-char(N) interaction, making contributions to effectively minimize NOx emissions in the future.

The electrochemical method has emerged as a novel option for bio-oil upgrading due to the advantages of having mild reaction conditions, control convenience and carbon neutrality. Bio-oil is easy to form coke even at low current densities during electrochemical upgrades of bio-oil. Unveiling the coke evolution during the electrochemical processing of bio-oil is essential to enable both oil-to-material and oil-to-fuel strategies. Here, we investigate the coke formation behaviors during the electrochemical processing of bio-oil. The coke comes primarily from the polymerization of aromatic components. The reaction time and current density have a promoting effect on the coke yields. The current density has an accelerating influence on the morphological evolution of the coke. The O-containing groups increases slightly with the increasing reaction time and current density. The large to small ring ratio of the coke is similar under different reaction time and current densities. The potential applications as carbon materials of the coke formed from bio-oil via electrochemical polymerization are discussed based on its physical morphology and chemical structure.

The W modified MnFe/Ti composite oxide catalyst was proposed and tested for low-temperature SCR of NOx by NH3, which possesses excellent SCR activity, N2 selectivity and SO2 tolerance compared with MnFe/Ti catalyst. The physicochemical properties of MnFeW/Ti catalyst were comprehensively characterized by N2 physisorption, XRD, Raman, XPS, NH3-TPD and H2-TPR. The transport of oxygen and electron became more facile during SCR reaction as a result of the formation of Mn-O-W and Fe-O-W bonds, which was beneficial to maintain the Mn4+, Fe3+ and chemisorbed oxygen at high relative concentrations and thus accelerated the SCR reaction rate. The appropriate acidity and redox property improved NOx conversion and N2 selectivity. The in situ DRIFTS results suggested that the surface acidity was tuned via the W doping, leading to that the SCR reaction obeys only Eley − Rideal mechanism. The TG-MS results and DRIFTS spectra revealed that the oxidation of SO2 can be inhibited by restraining the transfer of electrons from SO2 to Mn4+ and Fe3+, which reduced the formation of metal sulfates. Therefore, the MnFeW/Ti catalyst exhibits strong SO2 tolerance at low temperature.

This study focused on the interaction between organic solid waste (OSW) components on the formation and chemical composition of heavy components (>150 m/z) in OSW-oil. Rice husk (RH) and polypropylene (PP) as typical biomass and plastic fractions in OSW, were co-pyrolyzed at different blend ratios and different temperatures. The heavy components were characterized by FT-ICR MS, UV-F and GC MS. The results indicated that the yield of heavy components in PP-oil was higher than in RH-oil under the same temperature. Heavy hydrocarbons were found in PP-oil, while heavy phenols and heavy lipids existed in RH-oil. Significant interactions occurred at high temperatures (>600 °C). The interactions promoted the heavy components in all the blend-oils, corresponding to an increase of 20–35% compared to the calculated value of the content in PP-oil and RH-oil. At low PP ratio (25PP + 75RH), PP provided hydrogen to the reactive O-containing species in RH, leading to promoted heavy phenols and heavy lipids. At high PP ratio (50PP + 50RH and 75PP + 25RH), large aromatics (>3 rings) increased of 48–111% with respect to the calculated values. Plenty of PP‑hydrogen and a rich oxygen environment provided by RH radicals enhanced the formation of heavy aromatics and heavy PAH.

Nature Catalysis, 3, ISSN:2520-1158

Resolving atomic site-specific electronic properties and correlated substrate-molecule interactions is challenging in real space. Now, mapping of sub-10 nm sized Pt nanoislands on a Au(111) surface was achieved by tip-enhanced Raman spectroscopy, using the distinct Raman fingerprints of adsorbed 4-chlorophenyl isocyanide molecules. A spatial resolution better than 2.5 nm allows the electronic properties of the terrace, step edge, kink, and corner sites with varying coordination environments to be resolved in real space in one Pt nanoisland. Calculations suggest that low-coordinate atomic sites have a higher d-band electronic profile and thus stronger metal-molecule interactions, leading to the observed blue-shift of Raman frequency of the N≡C bond of adsorbed molecules. An experimental and theoretical study on Pt(111) and mono- and bi-atomic layer Pt nanoislands on a Au(111) surface reveals the bimetallic effect that weakens with the increasing number of deposited Pt adlayer.

Nitrogen (N)-doped nanocarbons (NDN) as metal-free catalysts have elicited considerable attention toward selective oxidation of alcohols with easily oxidizable groups to aldehydes in the past few years. However, finding a new NDN catalytic material that can meet the requirement of the feasibility on the aerobic catalytics for other complicated alcohols is a big challenge. The real active sites and the corresponding mechanisms on NDN are still unambiguous because of inevitable coexistence of diverse edge sites and N species based on recently reported doping methods. Here, four NDN catalysts with enriched pyridinic N species and without any graphitic N species are simply fabricated via a chemical-vapor-deposition-like method. The results of X-ray photoelectron spectroscopy and X-ray absorption near-edge structure spectra suggest that the dominating N species on NDN are pyridinic N. It is demonstrated that NDN catalysts perform impressive reactivity for aerobic oxidation of complicated alcohols at an atmospheric pressure. Eleven kinds of aromatic molecules with single N species and tunable π conjugation systems are used as model catalysts to experimentally identify the actual role of each N species at a real molecular level. It is suggested that pyridinic N species play an unexpected role in catalytic reactions. Neighboring carbon atoms in pyridinic N species are responsible for facilitating the rate-determining step process clarified by kinetic isotope effects, in situ nuclear magnetic resonance, in situ attenuated total reflectance infrared, and theoretical calculation. Moreover, NDN catalysts exhibit a good catalytic feasibility on the synthesis of important natural products (e.g., intermediates of vitamin E and K3) from phenol oxidation.

Supported metal nanoparticle catalysts are widely used in industry but suffer from deactivation resulting from metal sintering and coke deposition at high reaction temperatures. Here, we show an efficient and general strategy for the preparation of supported metal nanoparticle catalysts with very high resistance to sintering by fixing the metal nanoparticles (platinum, palladium, rhodium and silver) with diameters in the range of industrial catalysts (0.8–3.6 nm) within zeolite crystals (metal@zeolite) by means of a controllable seed-directed growth technique. The resulting materials are sinter resistant at 600–700 °C, and the uniform zeolite micropores allow for the diffusion of reactants enabling contact with the metal nanoparticles. The metal@zeolite catalysts exhibit long reaction lifetimes, outperforming conventional supported metal catalysts and commercial catalysts consisting of metal nanoparticles on the surfaces of solid supports during the catalytic conversion of C1 molecules, including the water-gas shift reaction, CO oxidation, oxidative reforming of methane and CO2 hydrogenation. Supported metal nanoparticles are indispensable catalysts in industry, yet they are often subjected to severe sintering. Now, a general method based on metal immobilization within zeolite is reported for the preparation of highly sinter-resistant catalysts for a broad range of industrially relevant processes.

By using an alpha-amino acid as an interfacial protector and pH adjustor, we demonstrate the synthesis of the long-range ordered mesoporous alumina (OMA) via a modified solvent evaporation induced self-assembly (EISA) method. Characterization results of XRD, TEM, and N2 adsorption-desorption indicate that the long-range highly ordered OMA was successfully obtained by using aluminum iso-propoxide as a precursor and Pluronic P123 as a template via the alpha-amino acid assisted EISA process. Moreover, by simply changing the alpha-amino acid, the textural property of the OMA was easily regulated, the extent of which depends on the molecular structure and coordination ability of the alpha-amino acid. The facile formation of the long-range highly ordered OMA was explained based on the function of the alpha-amino acids.

First-principles calculations are employed to study the optical properties of monolayer Te tuned by biaxial strain. Our results demonstrate that monolayer Te has strong absorption in the visible and ultraviolet regions, and that a structural transition occurs between the α-phase and the β-phase under certain strain. In addition, there is significant optical anisotropy in α- and β-Te, while γ-Te shows isotropic characteristics due to their different structural properties. Furthermore, strain has a significant impact on the optical properties. With increasing strain, the real and imaginary parts of the dielectric function exhibit redshift. In addition, the absorption spectrum is more likely to be excited under compressive strain rather than tensile strain in α- and β-Te, while only slight differences are induced in γ-Te. These findings can not only enhance the understanding of two-dimensional tellurium, but also provide an effective way to tune the optical properties for potential application in optoelectronic devices.

A simple, economic, efficient and eco-friendly nanodiamond (ND) modifying method to reinforce the ND/epoxy composite for the industrialization of the high-performance ND/epoxy composite is always desired. In the present work, the ND was successfully modified only using aqueous ammonia through an easy-to-operate method by replacing the hydrogen atoms in the carboxyl group with ammonium ions. Ammonia, which is the only pollutant in the process, could be recycled. The modified ND/epoxy composite showed an overwhelming advantage over the neat epoxy or the ND/epoxy composite in storage modulus in their glassy state without any degradation of tensile strength, hardness and fracture toughness.

Carbon is demonstrated as a mild and transition metal free catalyst for the preparation of N-rich heterocyclic compounds for the first time. The surface > C=O groups on nanodiamonds were identified as an active site, which most probably generates imidogene as a reactive species that triggers the reaction. The experimental results supported with density functional theory calculations were used to reveal a new reaction pathway, different from the conventional homogeneous one that indicates involvement of nitrogen radicals in the reaction.

Hybrid materials consisting of few-layer sp 2 carbon supported on Al 2 O 3 can potentially display comparable performance with nanodiamonds for the oxidative dehydrogenation of ethylbenzene. The hybrid structure could be easily prepared by fast coking method using ethanol as a precursor and ɣ-Al 2 O 3 with high specific surface areas as a template. In this case, ɣ-Al 2 O 3 plays the role of 3D support for depositing few-layer graphene-like structure. The hybrid structure exhibiting similar structure with nanodiamonds calcined at high temperature is further used as a metal-free catalyst for the oxidative dehydrogenation of ethylbenzene to styrene. The yield rate of styrene normalized by the specific area on Al 2 O 3 @C is 0.044 mmol m −2 h −1 (TOF = 4.13 h −1 ) which is two times of that on nanodiamonds (0.020 mmol m −2 h −1 , TOF = 3.27 h −1 ). Considering the low cost process and good catalytic performance, the hybrid nanostructure may be a promising candidate to be applied in the oxidative dehydrogenation of ethylbenzene.

Developing highly efficient, low-cost oxygen reduction catalysts, especially in acidic medium, is of significance toward fuel cell commercialization. Although pyrolyzed Fe-N-C catalysts have been regarded as alternatives to platinum-based catalytic materials, further improvement requires precise control of the Fe-Nx structure at the molecular level and a comprehensive understanding of catalytic site structure and the ORR mechanism on these materials. In this report, we present a microporous metal–organic-framework-confined strategy toward the preferable formation of single-atom dispersed catalysts. The onset potential for Fe-N-C is 0.92 V, comparable to that of Pt/C and outperforming most noble-metal-free catalysts ever reported. A high-spin Fe3+-N4 configuration is revealed by the 57Fe Mossbauer spectrum and X-ray absorption spectroscopy for Fe L-edge, which will convert to Fe2+-N4 at low potential. The in situ reduced Fe2+-N4 moiety from high-spin Ox-Fe3+-N4 contributes to most of the ORR activity due t...

As an eco-friendly, cheap and readily available material, calcium-based oxides could play the dual roles of both tar reforming catalyst and CO2 sorbent, thereby producing hydrogen-rich gas with low...

Pt nanoparticles (NPs) immobilized on a core-shell hybrid carbon support can deliver efficient direct dehydrogenation of n-butane at a lower temperature. The hybrid carbon support is composed of a nanodiamond core and a reinforced ultrathin graphene shell (ND@G), which improves the stability of anchored Pt NPs against sintering under reaction condition. The as-prepared Pt/ND@G catalyst demonstrates a distinguished catalytic performance (~25% conversion with >95% selectivity toward the olefins) at 450 oC for over 10 h as a result of the strong metal-support interaction between the Pt NPs and the hybrid carbon support. The catalyst can also be fully regenerated by a post oxidative thermal treatment.

Hybrid sp2/sp3 nanocarbons, in particular sp3-hybridized ultra-dispersed nanodiamonds and derivative materials, such as the sp3/sp2-hybridized bucky nanodiamonds and sp2-hybridized onion-like carbons, represent a rather interesting class of catalysts still under consideration. Their characteristics, properties and catalytic reactivity are presented, with an analysis of the state-of-the-art of their use in gas- and liquid-phase reactions, including photo- and electro-catalysis. It is remarked that intrinsic differences exist between these and other nanostructured carbon catalysts. The analysis shows how different features make nanocarbons unique with respect to other types of catalysts and are the bases for an advanced design of nanocarbon-type catalysts. The aspects discussed regard the presence of hybrid sp2/sp3 configurations, nano-engineering related to the role of defects and vacancies in their catalytic behaviour, the creation of active sites by modification in the charge density at carbon atoms or C–C bonds, the generation of strained C–C bonds by curvature and other mechanisms, and the formation of semiconducting areas and defect sites at the interface with supported nanoparticles. The advanced strategies for identifying and quantifying active sites of carbon catalysts are highlighted.

Doping with heteroatoms, such as nitrogen and boron, is crucial for the good performance of metal-free carbon cathode catalysts in the CO2 electrochemical reduction reaction (CERR). In this report, for the first time phosphorus is used to fabricate carbon catalysts and it is found that the bonding configuration of phosphorus has a key effect on the performance of the CERR. Two different phosphorus doped onion-like carbon (P-OLC) catalysts are synthesized with P–O bonding or P–C bonding as the major phosphorus bonding configuration, respectively. Compared to P-OLC with P–O bonding, P-OLC with P–C bonding exhibits a much better CERR performance, with a partial current density of 4.9 mA cm−2, 81% faradaic efficiency, and excellent durability (27 h) at low potential (−0.90 V vs. SHE). Density functional theory calculations show that the binding energy of the key intermediate COOH* in P–C bonding is much higher than that of its counterpart in P–O bonding, which is beneficial for lowering the energy barrier of the rate-limiting step. The better reactivity of the P–C bonding site is also verified by aromaticity analysis. Moreover, ultraviolet photoelectron spectroscopy (UPS) and partial density of state (PDOS) analysis suggest that the electron transfer capability of P–C bonding is stronger than that of P–O bonding. The current study demonstrates that phosphorus doping is an effective strategy for fabricating carbon CERR catalysts and reveals the pivotal role of the phosphorus bonding configuration.

Recent progress from first principles computational studies is presented for catalytic properties of nanostructured carbon catalysts in the oxidative dehydrogenation (ODH) reaction of short alkanes. Firstly, a brief introduction is given on the development of carbon catalysts in ODH since 1970. Oxygen functional groups have pivotal importance for ODH on nanostructured carbon catalysts. We discuss the oxidation process by HNO3 on pristine and defective carbon materials. The interactions between the oxygen molecule (oxidant) and the nanostructured carbon catalysts are quantitatively calibrated. Moreover the different nucleophilic abilities of oxygen functional groups are carefully compared and the strongest nucleophilic sites are proposed. The active sites and detailed reaction pathway are revealed from several computational studies. Diketone/quinone groups are generally considered to be the active centers in ODH. A reaction pathway via radical formation is considered as the favorable path. Furthermore, single ketone and carbon sites are verified to be active in ODH from the analysis of aromaticity. Heteroatom doping effects in ODH are examined. Nitrogen doping is found to be very reactive towards oxygen molecule activation. Other dopants such as boron, phosphorous and sulfur also have positive effects on the reactivity of ODH. Extensive calculations suggest that the BEP relation is applicable for the doped nanostructured carbon catalysts. In the end, an outlook for the future direction of the computational study is supplied.

Substituted polycyclic aromatic hydrocarbons released from sewage sludge pyrolysis bring the concern of the clean utilization for the waste. Herein, the roles of calcium oxide on the release of these compounds, especially the heavy ones containing nitrogen and oxygen atoms were investigated. The results showed that calcium oxide significantly decreased light substituted polycyclic aromatic hydrocarbons in the volatiles from 450 to 850 °C and showed obvious inhibitory effects on the formation of heavy substituted polycyclic aromatic hydrocarbons at 850 °C. To understand the impact mechanisms, pyrolysis experiments of sludge model compounds lipid, protein and polysaccharides were conducted. It was found that calcium oxide could catalyze or react with all three components to decrease the content of light substituted polycyclic aromatic hydrocarbons. Heavy oxygen-containing aromatics in sludge derived volatiles mainly resulted from polysaccharides and protein, and they considerably decreased after mixing with calcium oxide. Oxygen-containing aromatics content in the lipid derived volatiles, however, would increase due to polymerization reactions. The decreasing release of nitrogen substituted polycyclic aromatic hydrocarbons from sludge could be attributed to the synergy effects of CaO and other minerals or the effects of CaO on the interaction between protein and other organics.

The catalytic mechanism of Na during NO reduction on char surface is proposed to provide fundamental information for minimizing NOx emissions. A molecular modeling study was carried out using density functional theory to clarify the NO reduction and CO release pathways on char surface. The calculation results explain the promotion phenomenon caused by Na catalysis, and the fluctuation of the CO release curve in the experiment. Under H2O/Ar atmosphere, besides the NO-char heterogeneous reaction, simultaneous occurrence of the NO homogeneous reaction with lower energy barrier improved the NO reduction rate. According to the simulation results, the catalytic effect of Na is manifested in that it can weaken the conjugated components of the aromatics structure, and form a stable H-C-O-Na structure to weaken the connected C–C bond, thereby facilitating the CO release. Mayer bond order and RDG analyses indicate that the participation of Na can prevent the C-O bond from being stretched, and generate the strong attractive interaction to promote the NO reduction.

Four types of biomass-derived organics (toluene/1-methylnaphthalene/phenol/ethanol) were catalytically decomposed and steam reformed over Ni/α-Al2O3 for co-production of hydrogen and carbon nanotubes (CNTs). In the decomposition reaction, the oxygen functional group in phenol and ethanol promoted the co-production of hydrogen and CNTs, while a small amount of toluene and 1-methylnaphthalene were cracked to hydrogen and amorphous carbon. In the reforming reaction, the yields of hydrogen and CNTs sharply increased. More than 2000 mmol/(g-cata∗h) of H2 and 260 mg/(g-cata∗h) of CNTs were produced after the reforming of toluene and ethanol. However, 1-methylnaphthalene was difficult to be reformed and small amount of CNTs were formed. The organics with low molecular weight and low degree of unsaturation conduced to the formation of hydrogen and CNTs. The growth of CNTs on Ni/α-Al2O3 mainly follows the tip-growth mechanism. The diameter distribution of CNTs is not only influenced by Ni particle size, but also related to the different organics and steam addition.

Catalysts in the form of dispersed platinum nanoparticles (Pt NPs) immobilized on carbon usually suffer from deactivation through sintering under reaction conditions. In this contribution, we report the enhanced stability of highly dispersed Pt NPs on surface-modified carbon nanotubes (CNTs) against thermal and electrochemical sintering by N heteroatoms in the N-doped carbon support. The improved antisintering property of Pt NPs under thermal condition is characterized by in situ transmission electron microscopy (TEM), while the stability in electrochemical methanol oxidation reaction (MOR) is further examined at identical location (IL) using an advanced IL-TEM technique. A correlation of the Pt NP growth with the electrochemical surface area (ECSA) and the mass activity in MOR has been inferred. Our results indicate that both the surface oxygen groups and nitrogen-doped species are responsible for the fine dispersion of Pt NPs on the surface-modified CNTs, while the Pt NPs can be effectively stabilized u...

Biomass pellet is a popular fuel, and pyrolytic char can be a promised carbon material, further understanding char structural evolution can promote its utilization. To deeply investigate the evolution of char chemical structure and its heterogeneity during biomass pellet pyrolysis process, a new method was developed to fragment the char in space, and the chemical structures of the fragmented sections were analyzed by a micro-Raman spectroscopy (equipped with a 532 nm laser). The first-order Raman spectra (800–1800 cm−1) of varied positions of sawdust pellet pyrolytic char were curve-fitted with 10 Gaussian bands to reveal the temporal and spatial evolutions. The results indicate that pyrolysis of sawdust pellet can be divided into two stages: i) the decomposition of raw biomass (temperature heterogeneity in pellet remains); ii) the condensation reactions of aromatic ring systems (temperature in pellet becomes uniform). The axial and radial heterogeneity of char chemical structure is mainly caused by heat transfer when the whole pellet temperature is uniform during heating. While mass transfer, in accordance with volatile diffusion, can eliminate the heterogeneity of char chemical structure by volatile-char interaction. The combined effects of heat and mass transfer lead to a heterogeneity in pellet char chemical structure.

Sludge contains a high content of phosphorus (P) which makes the recovery of P from this material attractive. Inorganic apatite phosphorus (AP) could be utilized as a slow-release P fertilizer in a long term, thus transforming P-containing compounds into AP is greatly attractive. Herein, the migration and transformation behaviors of P from two municipal sewage sludge and a food-processing sludge were investigated during pyrolysis, and the effects of two calcium-based conditioners (CaO and CaCl2) on the formation of AP were explored. The results showed that nearly all P remained in sludge below 650 °C but around 22.5–49.0% P released from that at 850 °C, respectively. CaO helped retain phosphorus in sewage sludge at 850 °C, while CaCl2 facilitates its volatilization. Even though, the generation of AP was still improved under the effect of CaCl2. AP amount increased by 7.1–37.5% in food sludge derived char while AP amount increased by 7.3% to 21 times in sewage sludge derived char because of the two calcium-based conditioners. Model experiments showed that CaO could react with non-apatite inorganic phosphorus (NAIP) to generate calcium pyrophosphate and calcium orthophosphate, and CaCl2 could react with NAIP to form calcium pyrophosphate, calcium chlorapatite and phosphide. In general, CaCl2 exhibited a more excellent effect on the formation of AP than CaO while CaO showed more stable performance on the retention of TP.

Ce modified MnxOy/Al2O3-La have been prepared to investigate the effect of Ce loadings on pre-breakthrough H2S removal efficiency, breakthrough sulfur capacity (BSC) and BSC durability of the sorbents during desulfurization-regeneration cycles. The results showed Ce modification could improve the pre-breakthrough H2S removal efficiency of regenerated sorbents during desulfurization-regeneration cycles. The XPS characterization showed that the Ce can promote the binding energy of Mn ion to shift to lower energy, which enhanced H2S adsorption on the regenerated sorbent. However, the Ce loading sequence had effect on BSC durability of sorbent during desulfurization-regeneration cycles. The Ce-MnxOy/Al2O3-La with co-impregnation of Mn and Ce oxides had higher BSC than MnxOy/Al2O3-La, while the Ce/MnxOy/Al2O3-La with Ce loading on the surface of MnxOy/Al2O3-La had lower BSC and worse BSC durability than MnxOy/Al2O3-La. The characterization results showed Ce-MnxOy/Al2O3-La obtained better surface area and pore structure than MnxOy/Al2O3-La, and Ce ion can promote the increasing of the around electron density of Mn ion, which was beneficial for H2S adsorption of Ce-MnxOy/Al2O3-La. The poor surface area and pore structure would cause the low BSC of Ce/MnxOy/Al2O3-La, and less stability of pore structure might lead to poorer BSC durability of Ce/MnxOy/Al2O3-La than MnxOy/Al2O3-La during desulfurization-regeneration cycles.

Nanocarbon materials are promising catalysts of oxidative dehydrogenation (ODH) of alkanes, but improving the alkene selectivity remains a challenge. A deep understanding and thorough identification of oxygen species on nanocarbons are strongly required for approaches to nanocarbon modification. Successful application of iodometric titration in quantitative determination of the amount of electrophilic oxygen on the surface of carbon nanotubes has been performed in this work. Electrophilic oxygen species have been identified as the main culprits for deep oxidation of ODH of n-butane via a clear correlation between the amount of electrophilic oxygen and combustion reaction rate. By chemical reduction and annealing in nitrogen, the alkene selectivity is significantly improved. Phenol groups are found to play an essential role in improving alkene selectivity. The study reveals that higher alkene selectivity can be achieved by both eliminating deep oxidation active sites and facilitating the formation of pheno...

The reactivity of Zhundong chars is remarkably affected by the high sodium content of their parent Zhundong coal. The functional mechanism of inorganic sodium (NaCl) on the structure and reactivity of Zhundong chars was investigated in this study. Chars were prepared in a single-bed reactor under different pyrolysis temperatures and durations. Preliminary experimental results showed that inorganic sodium has a dual effect on the char yield of pyrolyzed Zhundong coal: inorganic sodium can decrease char yield at high pyrolysis temperatures of ≥600 °C but increase char yield at the low pyrolysis temperature of 400 °C. Nitrogen adsorption technique and scanning electron microscopy were utilized to identify the effects of inorganic sodium on the physical structure of Zhundong chars. The results showed that inorganic sodium affects pore structure detrimentally, inhibits the growth of char vesicles, and enables the formation of smooth char surfaces. Fourier transform infrared spectroscopy and Raman spectroscopy ...

The ultimate objective of chemical conversion is to achieve 100% selectivity from catalysis, and this is also a prodigious challenge for the conversion of light paraffins into olefins, because it involves controlled activation of highly stable aliphatic C-H bonds. Herein, we show that metal-free boron nitride (BN) nanosheets not only enable the oxidative dehydrogenation of ethane to ethylene exclusively at near 10% conversion, but they also deliver a remarkable 60% selectivity at an ethane conversion of 78% and remain stable over 400h at 575 degrees C. Our operando infrared spectroscopy and O-18 isotope tracer study explicitly demonstrates that B-O(H) active sites are formed at the edges of BN through the aid of ethane, and the dehydrogenation circle is completed over these B-O sites by the assistance of O-2.

The first-principle calculations are performed to explore the synergy effects between two dopants (N, S) and the detailed reaction pathway of oxygen reduction reaction (ORR) on the graphene catalysts. The co-doping N and S induces the significant spin density and has a strong chemical bonding with oxygen molecule which is not observed on the mono-doped cases. Three different reaction pathways are revealed from the calculations. Due to the large barrier of the O O breaking, the hydrogenation of the adsorbed oxygen molecule is kinetically more favorable. The free energy change of reaction under different electrode potential is also evaluated.

The varied surface structures of a Pd catalyst showed different catalytic performances in the partial hydrogenation of acetylene. The exposed Pd (1 0 0) facet is considered to be the most selective of all other facets for the formation of ethylene, but it is unstable and the fine structure needs to be revealed during the reaction. Herein, the evolution of the surface structure of cubic Pd nanoparticles, which are all bound with (1 0 0) facets, was studied by transmission electron microscopy in the partial hydrogenation of acetylene. Furthermore, the relation between the varying surface structure and the activity/selectivity was correlated. The (1 0 0) facets of Pd were transformed into stepped facets during the reaction, derived by adsorption/desorption of the reactants and energy compensation, which was the main reason for the decrease in the selectivity towards ethylene.

The surface activity and charged nature of ionic surfactants (sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB)) are used as in situ probes for the Coulombic nature of active sites in N-doped nanocarbon. In this report, we demonstrate that, by selectively masking charge-carrying sites, the active nitrogen sites in N-doped nanodiamond for oxygen reduction reaction are positively charged moieties, rather than those uncharged or negatively charged groups. From the N group analysis by X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption in a hydrogen gas atmosphere (H2-TPD), we put forth the concern that the active nitrogen groups in N-doped nanocarbon may contain oxygen and should not be simply classified by the four conventional nitrogen types by XPS binding energy.

Pd-based membranes play a critical role in the field of hydrogen purification and small-scale hydrogen generation. The microstructure and composition of ultra-thin Pd membranes immediately determines their performance and stability, which are however complex and elusive. We applied for the first time a novel technique of environmental scanning electron microscopy (ESEM) together with EDS analysis for in-situ investigation of microstructure and composition of Pd composite membranes under gas-thermal treatment. It enables step by step analysis of the evolution process and offers more meticulous details compared to ex-situ technologies through analysis at exactly the same location of membrane samples. Here we observed the elimination of Pd crystallites as well as the homogenization/diffusion along the whole membrane surface following high T treatment under inert gas or H 2 atmosphere. Gradual evolution of microhillocks on Pd membrane surface was resulted due to α−β phase transition or exposure to either O 2 or H 2 O, which can be effectively “smoothened” out during H 2 treatment. The exposure to steam exhibited a mild oxidation effect without pinhole formations, which appears a more appropriate surface cleaning process compared to air/oxygen treatment. A significant interlayer diffusion was revealed between Pd layer and ZrO 2 /alumina substrate in H 2 /O 2 /H 2 O atmosphere.

A study was carried out in both inert and CO2 atmosphere to investigate the interaction mechanism of K2CO3 with graphite and coal char during the catalytic gasification of coal char. The formation of K2CO3 catalytic precursors was identified by using series of different techniques. The results obtained in an inert atmosphere show that the interaction between K2CO3 and carbon readily took place at low temperature. For the K2CO3 loaded graphite, the intermediate of CnK clusters formed by the interactions of K2CO3 with carbon prevented the evaporation of K at low temperature. At temperatures above 800 °C, however, the CnK clusters were unstable, and decomposed to release K through vaporization. On the contrary, for the K2CO3 loaded demineralized coal char, due to the presence of oxygen groups, K was tightly bonded to carbon during heating, forming a complex precursor containing O and K with high thermal stability. The reaction pathway of carbon-K2CO3 interactions in an inert atmosphere are proposed for both char and graphite. The results of DRIFTs experiment suggest that CO2 is chemisorbed by the K- catalytic precursors during CO2 gasification to form potassium phenolate species and a covalently bound carbonate group (dimethyl carbonate). It is believed that these species act as active intermediates in the gasification process.