In this study, a reliable and steady PCDD/F generation system was utilized to investigate the performance of catalysts, in which 130 congeners of tetra- to octapolychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) vapors were studied under simulated flue gas with/without O3. TiO2 and carbon nanotubes (CNTs) supported vanadium oxides (VOX/TiO2–CNTs) modified with MnOX and CuOX, which were reported to be beneficial to the decomposition of model molecules, were found to have a negative effect on the removal of real PCDD/Fs in the simulated flue gas without O3. Moreover, the addition of MnOX presented different effects depending on whether CuOX existed in catalysts or not, which was also contrary to its effects on the degradation of model molecules. In an O3-containing atmosphere, low chlorination level PCDD/Fs congeners were removed well over VOX-MnOX/TiO2–CNTs, while high chlorination level PCDD/Fs congeners were removed well over VOX-CuOX/TiO2–CNTs. Fortunately, all PCDD/Fs congeners decomposed well over VOX-MnOX-CuOX/TiO2–CNTs. Finally, the effects of tetra- to octachlorination level for the adsorption and degradation behaviors of PCDD/Fs congeners were also investigated.

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.

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.

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.

Manganese oxide supported on carbon nanotubes (MnOx/CNTs) were prepared by an impregnation method and their catalytic oxidation performances of chlorobenzene (CB) with the assistance of ozone were investigated. The experimental results indicated a synergistic effect between the MnOx/CNTs catalyst and ozone promotion for CB destruction, which promoted CB oxidation at temperatures between 80 °C and 280 °C. Especially at temperatures below 120 °C, both CB conversion and CO2 selectivity above 95% were achieved with an apparent activation energy of 15.0 kJ mol−1. Moreover, MnOx/CNTs showed good stability and resistance to chlorine poisoning, which was demonstrated by stable catalytic activity for a long-term CB catalytic oxidation with 2300 ppm ozone up to 240 h.

Temperature-dependent effects of SO2 on selective catalytic reduction (SCR) of NO by NH3 over a TiO2 and carbon nanotubes (CNTs) supported iron–copper oxides catalyst were examined. At temperature below 300 °C, deposition of sulfites and sulfates on the catalyst surface suppressed NH3 adsorption, NO adsorption, and oxidation, which induced catalyst deactivation. The deposited sulfite/sulfates could be partially removed by 400 °C postannealing, which regenerated the catalyst. At temperature above 350 °C, NO adsorption was promoted by SO2 introduction, and suppression of NH3 adsorption also minimized the side reaction of NH3 oxidation, which increased the NO removal efficiency from 68% to 80% through reaction between adsorbed NO and gaseous NH3.

Ozone is found to promote the monochlorobenzene (CB) catalytic oxidation over carbon nanotubes supported copper oxide composite up to reaction temperature of 300 °C. Especially at 250 °C, a CB conversion of 99 %, together with a CO2 selectivity of 98 %, 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 250 °C.

The electronic structure and impurity states of S-doped cBN were investigated by first-principle approaches. Our calculation shows that S substituted for an N atom creates shallow donor levels merged to the states at the conduction band edge, S substituted for a B atom creates deep donor levels within the band gap, both forming n-type cBN, and band gap of S-doped cBN decreases with the increase of dopant concentration. Moreover, from the view of energy, S is more likely to be substituted for a B atom than an N atom.Highlights► We investigated electronic structure and impurity states of different S-doping levels in cBN crystal theoretically using LDA approach in the frame of DFT. ► Both theory and experiment indicate that S is more likely to be substituted for a B atom than an N atom. ► S substituted for an N atom creates shallow electron levels merged to the states at the conduction band edge, and S substituted for a B atom creates deep levels within the band gap, both forming n-type cBN.

A series of V2O5–CeOX/TiO2-carbon nanotube composites were prepared by sol–gel method and their catalytic activity for the reduction of NOX with NH3 was compared. V2O5CeOX/TiO2 (Ce/V = 9) achieved a NOX removal efficiency of 92% and 98% at 200 °C and 250 °C, respectively. SEM, XRD, XPS, BET, Raman, TPD and TPR were employed to probe the promotional effect of CeOX. The appearance of Ce3+ is found to increase chemisorbed oxygen thus facilitates the catalytic reduction of NOX. The poisoning effect caused by SO2 was found to depend on temperatures and gas velocity strongly. Moreover, the existence of excess oxygen was found to be essential (2% of O2 compared to 500 ppm NOX) to keep high SCR activity.Graphical abstractThe NOX removal efficiency and reaction rate coefficient increased upon introduction of CeOX into catalyst V2O5/TiO2-CNTs.Highlights► A series of V2O5–CeOX/TiO2-CNTs catalysts were synthesized by sol–gel. ► A catalytic promotional effect was observed by adding CeOX into V2O5/TiO2-CNTs. ► The reducibility, acidity, chemisorbed oxygen increased with introduction of CeOX.

Catalysts V2O5/TiO2–carbon nanotubes (CNTs) were prepared by hydrothermal method and their activity for catalytic oxidation of chlorobenzene (CB) was studied. A CB conversion efficiency of 45% with a CO2 selectivity of 80% was achieved over V2O5 (1.2 wt %)/TiO2–CNTs(8.6 wt %) at a temperature as low as 200 °C. It also has the highest removal efficiency of 95% at 300 °C. From the analysis of XRD, SEM, TEM, and TPR, the low-temperature activity of V2O5/TiO2–CNTs could be ascribed to the high SBET, good dispersion of V2O5, and the possible adsorption of CB by free surface of CNTs.

The authors demonstrate that the residual compressive stress in cubic boron nitride films could be relaxed by 1500 K post annealing in H2 atmosphere. According to the IR peak shifting, approximately 4.5 GPa stress was relaxed after 4 hours annealing. Thus film adhesion was improved significantly, cubic boron nitride films with a cubic phase concentration of 90% (vol%) and a thickness of more than 200 nm showed excellent stability and no delaminations were observed even after annealing for over 30 months in the open air, while films without annealing delaminated from substrates within 1 week. Moreover, the relaxation of the compressive stress is accompanied with cubic boron nitride d (111) interplanar distance broadening and corresponding IR peak intensities increasing.Highlights► High-quality cBN films were deposited on Si and quartz substrates. ► The intrinsic stress was relaxed by 1500 K annealing without destroying film structure ► cBN films have not delaminated for more than 30 months ► Stress relaxation is accompanied with IR peak intensities increasing.

MnOx/Al2O3-carbon nanotubes (CNTs) composites prepared by hydrothermal method were characterized by XRD, SEM, TEM, TGA, BET, XPS and H2-TPR. Catalytic oxidation of chlorobenzene (CB) was conducted over the composites under gas hourly space velocity (GHSV) of 36000 h−1 and CB concentration of 2800 ppmv. For the catalyst with approximately 25 wt% CNTs and 10 at.% Mn, CB removal efficiencies reached up to 83.3 and 97.7% at 150 and 300 °C, respectively. Moreover, no Cl species was detected over the used MnOx/Al2O3-CNTs catalyst implying that the release of chlorine element from the catalyst surface was facilitated by CNTs introduction.

Mn–Ce–OX catalysts loaded on TiO2-carbonaceous materials were prepared by sol–gel method. Selective catalytic reduction of NOX was conducted in a fixed-bed flow-reactor over catalysts coated on aluminum plates. A de-NOX efficiency of more than 90% was obtained over the Mn–Ce–OX/TiO2-carbon nanotubes (CNTs) catalyst between 75 °C and 225 °C under a gas hourly space velocity (GHSV) of ~ 36,000 h−1. This activity improvement is attributed to the increase of the BET surface area, and the occurrence of reaction between adsorbed NOX and NH3. Moreover, the de-NOX efficiency was increased to 99.6% by adding 250 ppm SO2 between 100 °C and 250 °C.Selective catalytic reduction of NOX with NH3 over Mn–Ce–OX catalysts loaded on TiO2-carbonaceous materials was conducted. The de-NOX efficiency was increased to 99.6% by adding 250 ppm SO2 between 100 °C and 250 °C. The given figure shows the NOX removal efficiency as a function of reaction temperatures over Mn–Ce/Ti-CNTs under different SO2 and/or NH3 concentrations. The data in bracket represent the concentrations (ppm) of NOX, NH3 and SO2, respectively.Download full-size imageHighlights► Carbon nanotubes (CNTs) were introduced into the traditional Mn–Ce–OX/TiO2 catalyst for the reduction of NOX with ammonia. ► The activity promotion at low-temperatures in Mn–Ce–OX/TiO2-CNTs catalyst could be attributed to the increase of BET surface area, and the occurrence of reaction between adsorbed NOX and NH3. ► The improvement of de-NOX efficiency in Mn–Ce–OX/TiO2-CNTs catalyst by introducing a small amount of SO2 is also observed. ► The flow-reactor used for catalytic activity tests was close to the real selective catalytic reaction (SCR) systems.

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.