Xiaobin Zhang

Synthesis of silicon nitride nanorods using carbon nanotube as a template

A method to prepare silicon nitride nanoscale rods using carbon nanotube as a template has been presented in this letter. The products of the reaction of carbon nanotubes with a mixture of Si and SiO2 powder in nitrogen atmosphere are β-Si3N4, α-Si3N4, and Si2N2O nanorods. The sizes of the nanorods are 4–40 nm in diameter and up to several microns in length. The formation mechanism of the nanorods has also been discussed.

Catalytic reduction of NOx with NH3 over different-shaped MnO2 at low temperature

MnO(2) nanotubes, nanorods, and nanoparticles were prepared using a hydrothermal method, after which the different activities for selective catalytic reduction (SCR) of nitrogen oxides (NO(x)) were compared. MnO(2) nanorods performed the highest activity for reduction of NO(x) under a gas hourly space velocity of 36,000 h(-1) with conversion efficiencies of above 90% between 250 and 300 °C; it also had the highest removal efficiency of 98.2% at 300 °C. From the analysis of X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, temperature-programmed desorption, and temperature-programmed reduction, we can ascribe the high activity of MnO(2) nanorods to low crystallinity, more lattice oxygen, high reducibility, and a large number of strong acid sites. The apparent activation energy of the SCR reaction on the surface of nanorods was calculated to be 20.9 kJ/mol, which favored the reaction better than the other catalysts.

Promotional effects of carbon nanotubes on V2O5/TiO2 for NOX removal.

A series of V(2)O(5)/TiO(2)-carbon nanotube (CNT) catalysts were synthesized by sol-gel method, and their activities for NO(X) removal were compared. A catalytic promotional effect was observed by adding CNTs to V(2)O(5)/TiO(2). The catalyst V(2)O(5)/TiO(2)-CNTs (10wt.%) showed an NO(X) removal efficiency of 89% at 300°C under a GHSV of 22,500h(-1). Based on X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, NH(3)-temperature-programmed desorption, temperature-programmed reduction, Brunauer-Emmett-Teller surface area measurements, differential scanning calorimetry, and thermogravimetric analysis, the increased acidity and reducibility, which could promote NH(3) adsorption and oxidation of NO to NO(2), respectively, contributed to this promotion.

Preparation of MnOx/TiO2 composites and their properties for catalytic oxidation of chlorobenzene

MnO(x)/TiO(2) composites with different atomic ratio of Mn/Ti were prepared by sol-gel, solvothermal and coprecipitation method, respectively. The catalytic tests on chlorobenzene (CB) removal ability of all 15 catalysts were performed in a fixed-bed flow reactor and compared to each other. Experimental results showed that when the atomic ratio of Mn/Ti reached 1:4, the activity of the catalysts prepared by three methods reached their highest value, particularly the catalyst with the Mn/Ti atomic ratio of 1:4 prepared by sol-gel method showed higher catalytic activity than the catalysts with the same atomic ratio prepared by other methods at temperature between 100 and 300 degrees C. From the microstructure characterization by XRD, SEM, EDS, BET, and TPR, it could be known that the combined TiO(2) phases of anatase and rutile and a good dispersion of manganese oxides contributed to a good catalytic performance in the catalyst prepared by the sol-gel method.

Low-temperature synthesis of high-ordered anatase TiO2 nanotube array films coated with exposed {001} nanofacets.

High-ordered anatase TiO2 nanotube array films coated with exposed high-reactive {001} nanofacets were fabricated by a modified hydrothermal method using amorphous anodic TiO2 nanotube arrays (ATONAs) as starting materials. It was found that the reaction between gas phase HF and solid ATONAs played a key role in the transformation process from amorphous to anatase TiO2, and the TiO2 tubular structure kept unchanged during the surface modification with an exposed {001} facets up to 76.5%, which could be attributed to the low reaction temperature of 130u2009°C. Our study provided a novel route for the facile preparation of {001} facets exposed anatase TiO2.

Selective catalytic reduction of NO by NH3 over CuO–CeO2 in the presence of SO2

SO2-induced deactivation of selective catalytic reduction of NO over CuO–CeO2 was studied. In the case of reaction under low O2 concentration of 1.0 vol%, SO2 severely deactivated the catalyst at 240 °C with a surface S atomic concentration as low as 1.34%. However, the deactivated catalyst could be reactivated during online NO reduction under 5.0 vol% O2 without decreasing the surface S concentration of the catalyst, which could be attributed to the involvement of NO2 in the reactions. NO2 could promote the NO removal through three reaction routes: fast SCR reaction, reaction between NO2 and NH3, and reaction between NO2 and NH4+. Especially under conditions of 10% O2, the reaction between NO2 and NH3/NH4+ induced the formation of extra NHX<3 species which promoted the decomposition of surface-deposited sulfate to SO2 with the assistance of Ce2O3, further suppressed the accumulation of sulfate on the catalyst surface, and finally suppressed the SO2-induced catalyst deactivation.

Influence of hexagonal boron nitride on the selective catalytic reduction of NO with NH3 over CuOX/TiO2

Hexagonal boron nitride (hBN) was used as a CuOX/TiO2 catalyst carrier and its effect on NO reduction with NH3 was studied. After hBN was treated with concentrated HNO3, CuOX/TiO2 nanoparticles were dispersed well onto hBN, and the addition of hBN was found to promote NO oxidation, while at the same time suppress NH3 oxidation to NO, and thus promoted the selective catalytic reduction of NO at reaction temperatures between 150 to 350 °C, and a high de-NOX efficiency of 90.6% was achieved at 275 °C. Our study indicates that hBN is a promising catalyst promoter and carrier with excellent stability compared to carbonaceous materials.

Ozone Promotion of Monochlorobenzene Catalytic Oxidation Over Carbon Nanotubes-Supported Copper Oxide at High Temperature

AbstractOzone is found to promote the monochlorobenzene (CB) catalytic oxidation over carbon nanotubes supported copper oxide composite up to reaction temperature of 300xa0°C. Especially at 250xa0°C, a CB conversion of 99xa0%, together with a CO2 selectivity of 98xa0%, was observed. The selective adsorption of CB, the promotion of Cu+ to Cu2+ oxidation, and the combination of O3 and high temperature activated gas phase O2 are all considered to attribute to the high CB conversion and CO2 selectivity at temperature above 250xa0°C.Graphical AbstractEffects of O3 on catalytic oxidation of CB over CuOX/CNTs were studied. A CB conversion of 99xa0% and a CO2 selectivity of 98xa0% were achieved at 250xa0°C, which could be mainly attributed to the synergy between the CB oxidation by O3 and activated O2.n

Mechanistic study of selective catalytic reduction of NO with NH3 over highly dispersed Fe2O3 loaded on Fe-ZSM-5

ZSM-5 supported highly dispersed FexOy clusters were prepared by a sol–gel method for selective catalytic reduction (SCR) of NO with NH3. XRD, SEM, UV-vis, H2-temperature-programmed reduction (H2-TPR), NH3-temperature-programmed desorption (NH3-TPD), and BET analyses all indicated that Fe species mainly existed as highly dispersed surface FexOy clusters with a Fe3+ concentration of 22 wt%. NO-temperature-programmed oxidation (NO-TPO) revealed that the FexOy clusters promoted the oxidation of NO to NO2, which promoted the low temperature NOX removal. NH3 was activated above 250 °C and over-oxidation of NH3 to NOX was not observed, as a result, a NOX removal efficiency of 91% was achieved at 400 °C. Moreover, the SCR reaction route was found to be temperature dependent, below 200 °C, the NOX reduction followed the reaction between NO2 and non-activated NH3. Fast SCR reaction dominated the NOX removal in the temperature window of 200–325 °C. At temperatures above 250 °C, the normal reaction between activated NH3 and NO compensated the thermodynamic limitation induced suppression of fast SCR.

Influence of the compressive stress on the infrared absorption of sp2-bonded boron nitride in cubic boron nitride thin films

Cubic BN films with a pure cubic phase upper layer were prepared by plasma-enhanced chemical vapor deposition. Infrared spectroscopy was applied to analyze the content of initial sp2-bonded BN layer in cubic BN thin films under compressive stress. It was found that the peak intensity near 1380cm−1 attributed to the B–N stretching vibration of sp2-bonded BN was suppressed by the compressive stress in cubic BN films. The deviation between the measured and calculated peak intensities was found to be linear with the compressive stress when the upper layer of the film is a pure cubic phase layer.