Salt-Supported Nickel Oxides for Boosted Hydrogen Production: The Critical Role of Halogen.

Hydrogen production from organic waste by gasification and reforming technologies offers major benefits to both the environment and climate. The long-term stability and regeneration of the reforming catalyst are still the biggest challenges because of carbon deposition. Here we report a recyclable salt-supported nickel oxide NiO/NaX (X: F, Cl, Br) catalyst for effective autothermal reforming of the oxygenated volatile organic compound (OVOC) ethyl acetate to hydrogen. The optimal hydrogen selectivity achieved 82.0% at 650 °C and the durability reached 43 h. Interestingly, with the decreasing of halogen electronegativity (F > Cl > Br) in NaX, the corresponding hydrogen selectivity of the catalysts decreased. Although NiO/NaX catalysts possess a very small specific surface area and a dense microstructure, their catalytic performance is better than that of normal Ni-based catalysts loaded on high-specific-surface-area supports. Detailed investigations revealed the critical roles played by halogen during the reforming reaction. First, the strong electronegative halogen in NaX induced the formation of hydrogen bonds with the reactants and reaction intermediates, which may prolong the surface residence time of such species, thus ensuring efficient hydrogen production over small-specific-surface-area catalysts under high-temperature conditions. Second, the halogen of the support NaX weakening the Ni-O bonds of the exposed Ni atoms in NiO/NaX made it easier for NiO to be reduced to Ni0, thus reducing the reaction activation energy and prompting the rapid catalytic reaction. The strength of such metal-support interaction can be easily modulated by varying the halogen electronegativity. This study provides a new prospect for the design of innovative recyclable heterogeneous catalysts with low specific surface area but high activity.

Resource utilization of high-concentration SO2 for sulfur production over La-Ce-Ox composite oxide catalyst.

Sulfur dioxide is one of the main causes of air pollution such as acid rain and photochemical smog, and its pollution control and resource utilization have become important research directions. La2O3 was incorporated into CeO2 to enhance the surface basicity of La-Ce-Ox catalyst and increase the concentration of chemisorbed oxygen, thereby promoting the improvement of catalytic performance of SO2 reduction by CO. Results have showed that the incorporation of La2O3 would not only increase the concentration of chemisorbed oxygen and hydroxyl on the catalyst surface, but also increase the basicity of the catalyst, thereby facilitating the adsorption of SO2 on the catalyst surface. The 12%La-Ce-Ox was the optimal catalyst, and its SO2 conversion at 350-400 ℃ reached close to 100%, and the sulfur yield at this temperature range was higher than 93%. Finally, according to the in situ infrared diffuse reflectance spectrum, it was found that the main reaction intermediates of 12%La-Ce-Ox in the catalytic reduction of SO2 were weakly adsorbed sulfate, SO32-, non-coordinating CO32-, monodentate carbonate, and CO, so the catalytic reaction followed the L-H and E-R mechanisms simultaneously.

Simultaneous catalytic removal of NO, mercury and chlorobenzene over WCeMnOx/TiO2-ZrO2: Performance study of microscopic morphology and phase composition.

Nitrogen oxides, mercury and chlorobenzene are important air pollutants emitted by waste incineration and other industries. Coordinated control of multiple pollutants has become an important technology for air pollution control. Through solid-phase structure control, the catalytic performance of the WCeMnOx/TiO2-ZrO2 catalyst for simultaneous catalytic removal of NO, mercury and simultaneous removal of NO and chlorobenzene were improved. MnWO4 improved the solid acidity of the catalyst and improved the catalytic activity at high temperature. The formation of Ce0·75Zr0·25O2, Ce2WO6, Ce2Zr2O7 and Ce2Ti2O7 improved the catalytic activity at low temperature. The presence of TiOSO4 would affect the valence of metal ions and the reduction of chemisorbed oxygen, thereby reducing the catalytic activity at low temperature. Within the same size range of nanoparticles, cyclic nanoparticles exposed more active sites due to their hollow structure, and their catalytic performance was better than spherical nanoparticles. The thickness of the circular nanoparticles of WCM/TZ-14 catalyst was about 14 nm, and the diameter was about 40 nm Ce0.75Zr0.25O2 and MnWO4 were also present in the phase composition. Therefore, it exhibited the best performance for simultaneous catalytic removal of NO, mercury and simultaneous removal of NO and chlorobenzene. The coincidence temperature window was 347-516 °C. Finally, WCM/TZ-14 catalyst followed both E-R and L-H mechanisms in the NH3-SCR reaction.

An Interface Optimization Strategy for g-C3N4-Based S-Scheme Heterojunction Photocatalysts.

Graphitic carbon nitride (CN) has attracted much attention in photocatalytic fields due to its unique electronic band structure. However, the rapid recombination of photogenerated carriers severely inhibits its catalytic activity. The heterojunction structure has been widely confirmed to significantly improve the photocatalytic activity of CN through the formed interface structure. However, researchers often give attention to the band matching and conductivity of the cocatalyst, while the importance of the interface as a migration channel for photogenerated carriers is often overlooked. In this work, we adopt the strategy of morphology engineering to regulate the morphology of the CN photoactive component so as to achieve the interface optimization of the traditional heterojunction structure. The photocatalytic degradation experiment of rhodamine B shows that compared with the traditional CeO2@CN heterojunction structure, the photocatalytic activity of the interface-optimized CeO2/CN is increased by more than 20%. The following points could be used to explain the improvement of photocatalytic activity: (I) the formed S-scheme heterojunction structure, which inhibits the recombination of useful electrons and holes but expedites the recombination of relatively useless electrons and holes, (II) the increased interface area, which provides more carrier migration channels, and (III) the reduced interface contact resistance, which facilitates the separation and migration of photogenerated carriers. Furthermore, the interface optimization of the traditional Al2O3@CN and Fe2O3@CN heterojunction structures also achieved consistent results. This shows that the strategy in this work is a universal method for interface optimization, which provides potential alternative for further improving the catalytic activity of other heterojunction composites.

Cobalt and nitrogen co-doped mesoporous carbon for electrochemical hydrogen peroxide sensing: the effect of graphitization.

In this study, a facile strategy for the scalable synthesis of cobalt and nitrogen co-doped mesoporous carbon (Co-N/C) is reported. Structural characterization demonstrated that Co and N were successfully co-doped in the highly porous carbon. Graphitization of porous carbon was achieved by the introduction of cobalt species. The degree of graphitization of Co-N/C could be further promoted by increasing the calcination temperature. By taking advantage of the excellent mass and electron transfer kinetics attributed to the high specific surface area, high porosity and high graphitization, the obtained Co-N/C exhibited good electrochemical activity towards H2O2 reduction and excellent sensing performance for the electrochemical detection of H2O2. The Co-N/C-950 catalyst obtained at 950 °C showed good electrochemical sensing performance with a detection limit of 2 µM and a wide linear response over the concentration range from 0.03 mM to 13 mM. Meanwhile, Co-N/C exhibited high selectivity toward the detection of H2O2 in the presence of possible interferences during the applications such as NaCl, glucose, ascorbic acid and so on. The results confirm that Co-N/C could be used as an efficient electrocatalyst to fabricate electrochemical sensing devices.

Smart paper transformer: new insight for enhanced catalytic efficiency and reusability of noble metal nanocatalysts.

Although noble metal nanocatalysts show superior performance to conventional catalysts, they can be problematic when balancing catalytic efficiency and reusability. In order to address this dilemma, we developed a smart paper transformer (s-PAT) to support nanocatalysts, based on easy phase conversion between paper and pulp, for the first time. The pulp phase was used to maintain the high catalytic efficiency of the nanocatalysts and the transformation to paper enabled their high reusability. Herein, as an example of smart paper transformers, a novel chromatography paper-supported Au nanosponge (AuNS/pulp) catalyst was developed through a simple water-based preparation process for the successful reduction of p-nitrophenol to demonstrate the high catalytic efficiency and reusability of the noble metal nanocatalyst/pulp system. The composition, structure, and morphology of the AuNS/pulp catalyst were characterized by XRD, TGA, FE-SEM, ICP, TEM, FT-IR, and XPS. The AuNS/pulp catalyst was transformed into the pulp phase during the catalytic reaction and into the paper phase to recover the catalysts after use. Owing to this smart switching of physical morphology, the AuNS/pulp catalyst was dispersed more evenly in the solution. Therefore, it exhibited excellent catalytic performance for p-nitrophenol reduction. Under optimal conditions, the conversion rate of p-nitrophenol reached nearly 100% within 6 min and the k value of AuNS/pulp (0.0106 s-1) was more than twice that of a traditional chromatography paper-based catalyst (0.0048 s-1). Additionally, it exhibited outstanding reusability and could maintain its high catalytic efficiency even after fifteen recycling runs. Accordingly, the unique phase switching of this smart paper transformer enables Au nanosponge to transform into a highly efficient and cost-effective multifunctional catalyst. The paper transformer can support various nanocatalysts for a wide range of applications, thus providing a new insight into maintaining both high catalytic efficiency and reusability of nanocatalysts in the fields of environmental catalysis and nanomaterials.

Novel porous ceramic sheet supported metal reactors for continuous-flow catalysis.

A novel porous ceramic sheet supported nickel particles reactor was obtained by an in-situ preparation method. This reactor was then used to investigate continuous-flow catalysis of nitroaromatic compounds and methyl orange. The details of the structure and morphology were characterized by XRD, SEM, XPS, Raman, element mapping, mercury intrusion method and Archimedes principle. The porous ceramic sheet supported Ni particles reactor exhibited excellent catalytic performance in the catalytic reduction of p-nitrophenol and methyl orange by sodium borohydride at room temperature. Both the conversion of p-nitrophenol (5 mM) and methyl orange (0.3 mM) reached nearly 100% at the injection speed of 2.67 mL·min-1. In addition, it maintained conversions of 100% after 10 recycling time since the porous ceramic sheet could reduce the aggregation for Ni particles. Furthermore, the chemisorbed oxygen, and the strong interaction between Ni and porous ceramic sheet resulted in a highly efficient, recoverable, and cost-effective multifunctional reactor. All of these advantages present new opportunities to be implemented in the field of waste water treatment and environmental toxicology. Ultimately, the porous ceramic sheet could also support other metal nanomaterial, and used in other fields of environmental catalysis.

Strong interaction between Au nanoparticles and porous polyurethane sponge enables efficient environmental catalysis with high reusability.

A novel and recoverable platform of polyurethane (PU) sponge-supported Au nanoparticle catalyst was obtained by a water-based in-situ preparation process. The structure, chemical, and morphology properties of this platform were characterized by XRD, TGA, SEM, FT-IR, and XPS. The Au/PU sponge platform exhibited excellent catalytic performances in catalytic reductions of p-nitrophenol and o-nitroaniline at room temperature, and both catalytic reactions could be completed within 4.5 and 1.5 min, respectively. Furthermore, the strong interaction between Au nanoparticles and the PU sponge enabled the catalyst system to maintain a high catalytic efficiency after 5 recycling times, since the PU sponge reduced the trend of leaching and aggregation of Au nanoparticles. The unique nature of Au nanoparticles and the porous PU sponge along with their strong interaction resulted in a highly efficient, recoverable, and cost-effective multifunctional catalyst. The AuNP/Sponge nanocatalyst platform has great potential for wide environmental and other catalytic applications.

Resource utilization of waste V2O5-based deNOx catalysts for hydrogen production from formaldehyde and water via steam reforming.

The harmless disposal of abandoned and toxic V2O5(WO3)/TiO2 (VWT) deNOx catalysts has become a worldwide great demand, a new resource path for hydrogen production from steam reforming of formaldehyde and water using the waste VWT deNOx catalysts as catalyst carriers was proposed. The waste V2O5-based catalysts supported NiO (N/VWT) catalysts prepared by impregnation method were comparatively studied for hydrogen production. The H2 and CO selectivity of the optimum N/VWT separately reached 100% and 72.5%, and the formaldehyde conversion of the N/VWT reached 86.3% at 400 ℃ and higher than 93.0% at 450-600 ℃. Analysis showed that the hydroxyl species played the most important role, and its richness determined the catalytic performance directly. The high acid sites and excellent redox properties were beneficial to enhance the catalytic performance. The in situ DRIFT study verified that the hydrogen bonds between formate species and hydroxyl groups reduced reaction steps, which accelerated the progress of the reaction. The adsorbed formaldehyde transformed to formate species firstly, and then produced H2 and CO2 (or CO) by dehydrogenation. Ultimately, the resource utilization path not only completely solved the harmless problems of the waste V2O5-based deNOx catalysts and formaldehyde, but also contributed to the hydrogen production.

Novel TiO2 catalyst carriers with high thermostability for selective catalytic reduction of NO by NH3.

A series of TiO2 catalyst carriers with ceria additives were prepared by a precipitation method and tested for selective catalytic reduction (SCR) of NO by NH3. These samples were characterized by XRD, N2-BET, NH3-TPD, H2-TPR, TEM, XPS and in situ DRIFTS, respectively. Results showed that the appropriate addition of ceria can enhance the catalytic activity and thermostability of TiO2 catalyst carriers significantly. The maximum catalytic activity of Ti-Ce-Ox-500 is 98.5% at 400 °C with a GHSV of 100 000 h-1 and the high catalytic activity still remains even after the treatment at high temperature for 24 h. The high catalytic performance of Ti-Ce-Ox-500 can be attributed to a series of superior properties, such as larger specific surface area, more Brønsted acid sites, more hydrogen consumption, and the higher proportion of chemisorbed oxygen. Ceria atoms can inhibit the crystalline grain growth and the collapse of small channels caused by high temperatures. Furthermore, in situ DRIFTS in different feed gases show that the SCR reaction over Ti-Ce-Ox-500 follows both E-R and L-H mechanisms.

Heteroatom-Doped Graphene for Efficient NO Decomposition by Metal-Free Catalysis.

N, S, and B-doped graphene was fabricated by thermally treating graphene oxide with heteroatom-containing precursors and its catalytic behavior for NO decomposition reaction was evaluated. For the first time, the feasibility for heteroatom-doped graphene to be effectively used for decomposing NO was experimentally confirmed. The activity of different heteroatom-doped graphene follows the order: N-doped graphene > S-doped graphene > B-doped graphene. The electronegativity difference, specific area, and unique functional groups (pyridinic N and thiophene S) of the heteroatom-doped graphene play a crucial role in the catalytic performance. Furthermore, the effect of pyridinic N and thiophene S on the reaction mechanism was proposed. Pyridinic N and thiophene S can transfer extra electrons into π-antibonding orbit of NO, thus weakening N-O bond.

Key Role of Lanthanum Oxychloride: Promotional Effects of Lanthanum in NiLaOy /NaCl for Hydrogen Production from Ethyl Acetate and Water.

The hydrogen economy is accelerating technological evolutions toward highly efficient hydrogen production. In this work, the catalytic performance of NiO/NaCl for hydrogen production via autothermal reforming of ethyl acetate and water is further improved through lanthanum modification, and the resulted 3%-NiLaOy /NaCl catalyst achieves as high as 93% H2 selectivity and long-term stability at 600 °C. The promoting effect is caused by the strong interactions between lanthanum and NiO/NaCl, by which LaNiO3 and a novel LaOCl phase are formed. The key role of LaOCl in promoting low-temperature hydrogen production is highlighted, while effects of LaNiO3 are well known. The LaOCl (010) facet possesses high adsorption capacity toward co-chemisorbing ethyl acetate and water. LaOCl strongly interacts with ethyl acetate and H2 O in the form of hydrogen bonding and coordination effect. The interactions induce tensions inside ethyl acetate and H2 O, activate the molecules, and hence decrease the energy barrier for reaction. In situ Fourier transform infrared spectroscopy (FTIR) reveals that LaOCl along with NaCl enhances the adsorption ability of NiO/NaCl. Moreover, LaOCl improves the dispersion of Ni species in NiO-LaNiO3 -LaOCl nanosheets, which possess abundant active sites. The effects together promote hydrogen evolution. Furthermore, the NiLaOy /NaCl catalyst can be easily reborn after deactivation due to the water solubility of NaCl.

Mesoporous TiO2-SiO2 adsorbent for ultra-deep desulfurization of organic-S at room temperature and atmospheric pressure.

Ultra-deep desulfurization is a major requirement for upgrading the quality of fuel and power sources for fuel-cells. A series of mesoporous TiO2-SiO2 adsorbents were prepared and investigated for ultra-deep adsorption of benzothiophene (BT) and dibenzothiophene (DBT) from model fuel at ambient conditions. The adsorbents were characterized via SEM, XRD, N2-BET, FT-IR and NH3-TPD techniques. The results revealed that the adsorbent containing 40 wt% silica achieved the desulfurization efficiency higher than 99% when the initial sulfur concentration in the model fuel was 550 ppm. The high desulfurization performance of the adsorbent was attributed to its large specific surface and surface acidity. It also achieved a high sulfur adsorption capacity of 7.1 mg g-1 in a fixed-bed test, while its static saturated sulfur capacity was 13.7 mg g-1. The order of selectivity towards the adsorption of different organic sulfurs was DBT > BT&DBT > BT. The kinetics of the adsorption of organic sulfur was studied and the results indicated that the pseudo-second order model appropriately fitted the kinetics data. Furthermore, the used adsorbent can be easily regenerated and the desulphurization efficiency of the recovered adsorbent after five regeneration cycles was still maintained at 94.5%.

Novel CeMo x O y -clay hybrid catalysts with layered structure for selective catalytic reduction of NO x by NH3.

A facile method is to prepare novel CeMo x O y -clay hybrid catalysts with layered structures by using organic cation modified clay as support. During the preparation process, cerium cations and molybdate anions are easily adsorbed and impregnated into the interlamellar space of the organoclay, and after calcination they undergo transformation to highly dispersed CeMo x O y nanoparticles within the interlamellar space of the clay. As expected, the prepared CeMo0.15O x -OC-T catalysts with layered structures had high selective catalytic reduction (SCR) activity such as high NO x conversion of >90% in the wide temperature range of 220-420 °C. Meanwhile, they also exhibit high stability and tolerance to water vapor (5 vol%) and SO2 (200 ppm), demonstrating that these novel catalysts could serve as a good alternative for NH3-SCR in practical application.

Ultrastrong composite film of Chitosan and silica-coated graphene oxide sheets.

Chitosan (CS) has attracted significant interest in various fields due to its outstanding functional properties (especially, its chain with positive charge). However, wide-range applications of CS are severely limited because of its poor mechanical properties. Ultrastrong composite film of CS and silica-coated graphene oxide sheets (GO@SiO2) were prepared by a simple solution casting method in this article. GO@SiO2 was prepared by the hydrolysis of tetraethyl orthosilicate (TEOS) in GO ethanol solution. Compared with the pure CS film, the tensile strength of the CS/GO@SiO2 composite film with incorporation of 1.75wt% GO@SiO2 fillers was significantly increased 158% from 55±4 to 142±24MPa. Such high tensile strength may be caused synergistically by strong interaction between two components and high crystallinity of the CS matrix. CS based composite with ultrastrong strength may have more potential applications in biomedical fields.

Effect of fluorine additive on CeO2(ZrO2)/TiO2 for selective catalytic reduction of NO by NH3.

A series of CeO2(ZrO2)/TiO2 catalysts with fluorine additive were prepared by impregnation method and tested for selective catalytic reduction (SCR) of NO by NH3. These samples were characterized by XRD, N2-BET, Raman spectra, SEM, TEM, NH3-TPD, H2-TPR and XPS, respectively. Results showed that the optimal catalyst with the appropriate HF exhibited excellent performance for NH3-SCR and more than 96% NO conversion at 360°C under GHSV of 71,400h-1. It was found that the grain size of TiO2 increased and the specific surface area reduced with the modulation of HF, which was not good for the adsorption of gas molecule. However, the modulation of HF exposed the high energy (001) facets of TiO2 and increased the surface chemisorbed oxygen concentration, oxygen storage capacity and Ce3+ concentration of catalyst. In addition, the synergy of (101) and (001) facets was beneficial to the improvement of catalytic activity.