Graphical Reaction pathway ? More adsorption of NH 3 /NH 4 + species and the higher reactivity with gaseous NO maintain the process of E−R reaction path, leading to a satisfactory SCR activity of K poisoned NbFeVO x /TiO 2 . Whereas the decreased adsorption and reactivity of NH 3 /NH 4 + and NO x restrains the process of L−H reaction path, thus showing inferior SCR activity of K poisoned FeVO 4 /TiO 2 . FeVO 4 -based catalysts with a wide temperature window and high SO 2 tolerance have attracted increasing attention for the selective catalytic reduction of NO x with NH 3 . However, the alkali-resistance of FeVO 4 -based catalysts is still challenging. In this study, the K-resistance of FeVO 4 /TiO 2 was markedly improved via the Nb modification. It was demonstrated that the adsorption and reactivity of NH 3 /NH 4 + and NO x species on K poisoned FeVO 4 /TiO 2 both decreased, which restrained the process of Langmuir-Hinshelwood reaction path. As a comparison, more adsorption of NH 3 /NH 4 + species and the higher reactivity with gaseous NO maintain the process of Eley-Rideal reaction path, leading to a satisifactory SCR activity. This work demonstrated an effective route to improve alkali-resistance via modulating reactivity and reaction path of adsorbed NH 3 /NH 4 + and NO x species over Nb modified vanadate catalysts, which presented a new point for the development of high-performance alkali-resistant SCR catalysts.
Yi-Ning Huang,Mengyan Liu,Chenyang Ye,Huajie Luo,Ji Zhang,Dmitry V. Karpinsky,Shan-Tao Zhang,Yaojin Wang
Ceramic-based dielectric capacitors have gained prominence in research owing to their high relative permittivity, excellent mechanical properties, and temperature stability. BiFeO 3 -based ceramics have captured significant attention in dielectric capacitors attributable to their high saturation polarization. Yet, the high remanent polarization, as well as the low electric breakdown strength, constrains the improvement of their energy storage performances. Herein, we incorporated the A-/B-site complicated component (La 0.5 Na 0.5 )(Mg 1/3 Nb 2/3 )O 3 into the binary solid solution 0.7BiFeO 3 –0.3BaTiO 3 ceramics with morphotropic phase boundary, to enhance the endurance for electric field and reduce remanent polarization by optimizing relaxor behavior. Consequently, a high recoverable energy density of 8.3 J/cm 3 and a high efficiency of 84.6% under 500 kV/cm were obtained in the preferred composition. These results offer a feasible pathway to exploit the high-performance BiFeO 3 -based ceramics for electrostatic energy storage.
Co 3 O 4 catalysts possess high activity in selective catalytic oxidation of NH 3 (NH 3 -SCO), but the low N 2 selectivity hinders their potential application. To enhance N 2 selectivity, the chemical bonded Nb-O-Co catalyst by the deposition of Nb species onto Co 3 O 4 (Nb/Co 3 O 4 -0.03) is constructed. It shows 100 % NH 3 conversion and 82 % N 2 selectivity at 180°C, and the N 2 selectivity is 2.2-fold higher than that of Co 3 O 4 (38 %). The failure of enhancement in N 2 selectivity for physically mixed Co 3 O 4 and NbO x (NbO x |Co 3 O 4 -0.03) further indicates the crucial role of chemical bonded Nb-O-Co in enhancing N 2 selectivity. In situ diffuse reflectance infrared Fourier transform spectra and NH 3 temperature-programmed desorption results show the formation of new NH 3 adsorption sites. Importantly, intermediates NO - stabled on Nb/Co 3 O 4 -0.03 tends to react with -NH 2 to produce N 2 through internal selective catalytic reduction (iSCR). This work offers insights into enhancing the N 2 selectivity in NH 3 -SCO and advances understanding of iSCR mechanism.
In this paper, a series of Nb modified Cu-Ce-Ti mixed oxides (Nb y CCT) were synthesized using wetness impregnation method for the selective catalytic reduction of NO with ammonia (NH 3 -SCR). The activity tests indicated that Nb y CCT catalysts had shown superior SCR performances. Among which, Nb 0.05 CCT catalyst exhibited a NO conversion of more than 90% within a broad operation temperature window (180–360 °C) under the GHSV of 40,000 h −1 . After that, corresponding characterizations were performed to correlate the physical structures and surface properties to catalytic performances. These results revealed that the strong interactions among the active phases induced by Nb addition could not only enhance the redox property of the catalysts but also inhibit the over-oxidation of NH 3 , which would be beneficial to SCR performance within a wide temperature range and good reaction selectivity. Furthermore, DRIFTS results suggested that the doping of Nb could promote the formation of NO 2 , thereby enhancing the “fast” SCR reaction process (Langmuir-Hinshelwood reaction pathway). Moreover, the Nb 0.05 CCT catalyst showed a better sulfur tolerance compared to Nb free catalyst that over 85% NO conversion could be retained after 12 h SCR reaction in the presence of SO 2 and H 2 O.
危险品化学品经营许可证（带存储）