RESUMO
To reduce the number of microcracks and pores on the surface of laser cladding layers, we used a novel, to the best of our knowledge, surface alloying method to modify the surface of a NiCoCrAlY laser cladding coating using high-current pulsed electron beam technology. The x-ray diffraction peaks of the irradiated coatings were affected by the residual stress, which caused the peaks to shift and significantly broaden. With an increase in the number of pulses, the cleaning effect of the coating surface became significant. At the same time, the degree of surface alloying increased, and different degrees of slip were formed on the surface of the coating. There were many nanocrystals accumulated at the slip angle, and the grain size of the coating surface increased.
RESUMO
NOx emissions are a major environmental problem, and the selective catalytic reduction (SCR) is the most effective method to convert NOx in flue gas into harmless N2 and H2O. In this work, a new carrier, CuCeOy microflower assembled from a large number of copper-cerium mixed oxide nanosheets, is firstly developed to load vanadium-tungsten mixed oxides (VWOx) for the SCR of NOx with NH3. The resultant optimal VWOx/CuCeOy catalyst exhibits significantly enhanced low-temperature de-NOx performance with the NOx conversion of 60% at 180 °C, over 90% from 240 °C to 390 °C under the gas hourly space velocity (GHSV) of 36,000 h-1. The reason can be mainly attributed the fact that the transfer of electrons among Ce, Cu and V ions is very easy to occur via the following equations Ce3++Cu2+ â Ce4++Cu+, V5+ + Cu+ â V4+ + Cu2+, V4+ + Ce4+ â V5+ + Ce3+, which effectively decreases the apparent activation energy (Ea = 16.59 kJ/mol) of NH3-SCR de-NOx reaction. In addition, the enhanced reducibility and a large number of Brønsted acid sites also contribute the low-temperature de-NOx performance. Both Eley-Rideal and Langmuir-Hinshelwood mechanisms are included in the NH3-SCR de-NOx reaction over the VWOx/CuCeOy catalyst.