Selective Catalytic Reduction of NOx by CO over Doubly Promoted MeMo/Nb2O5 Catalysts (Me = Pt, Ni, or Co)

Abstract

Doubly promoted MeMo/Nb2O5 catalysts, in which Me = Pt, Ni, or Co oxides were prepared for the selective catalytic reduction of NOx by CO reaction (CO-SCR). Comparable chemical, textural, and structural analyses revealed similarities between NiMo and CoMo impregnated on Nb2O5, in contrast to PtMo sites, which were not homogeneously dispersed on the support surface. Both the acid function and metal dispersion gave a synergistic effect for CO-SCR at moderate temperatures. The reactivity of PtMo catalysts towards NOx and CO chemisorption was at low reaction temperatures, whereas the NOx conversion over CoMo was greatly improved at relatively high temperatures. Careful XPS, NH3-TPD, and HRTEM analyses confirmed that the large amounts of strong and moderate acid sites from PtOx entrapped on MoO3 sites induced high NOx conversions. NiMo/Nb2O5 showed poor performance in all conditions. Poisoning of the MeMo sites with water vapor or SO2 (or both) provoked the decline of the NOx conversions over NiMo and PtMo sites, whereas the structure of CoMo ones remained very active with a maximum NOx conversion of 70% at 350 °C for 24 h of reaction. This was due to the interaction of the Co3+/Co2+ and Mo6+ actives sites and the weak strength Lewis acid Nb5+ ones, as well.

Noble Metal Nanoparticles Decorated Boron Nitride Nanotubes for Efficient and Selective Low-Temperature Catalytic Reduction of Nitric Oxide with Carbon Monoxide

“…Reduction of metal nanoparticles is assumed to be produced by the sonolysis of metal precursors based on the cavitation effects. 24,49 The adhesion behavior of metal nanoparticles on BNNT is similar to the previously reported results even with the different supports, surface metals, and synthesis methods. 50,51 The TEM images for Pd/BNNT (panels a and b of Figure 2) showed that aggregated Pd nanoparticles are located at the surface of the BNNT.…”

“…29,31−35 Among different support materials, it was reported that the BN materials exhibit excellent stability and catalytic efficiency when combined with metal nanoparticles. 24,36 The excellent remedy of the defects and vacancies in BN-based materials using CO and NO gases also correlates with their good adsorption properties. 37,38 Hence, BN-based materials are worth considering as an affordable catalyst for enhancing the NO + CO reaction.…”

“…The platinum group metals (PGMs) show outstanding activity and good N 2 selectivity for the NO reduction and CO oxidation reactions. − However, the continuous increase in their price led researchers to find a cost-effective alternative catalyst for NO remediation. − Hence, alternative transitions metals, like Co-, Ni-, Cu-, and Fe-based composites, were explored as catalysts for NO + CO reactions, , although these transition metals have exhibited good catalytic efficiency and poor selectivity and stability, especially at high temperature ranges, as the limiting factors. − Another approach could be lowering the PGM loading or using a combination of PGMs and other metals. − Regardless, the catalytic activity of metal nanoparticles can be controlled by particle sizes and shapes of metallic nanoparticles, oxidation states, surface topology, and the interaction between surface species and support materials. − …”

Effects of the Incorporation of Distinct Cations in Titanate Nanotubes on the Catalytic Activity in NOx Conversion

“…In response to the contradiction, the current result illustrates that the expected NTs performance with NO x conversion is superior to 20%, even upon steam introduction ( Figure 7 a). Thus, moisture interacts with the surface of the NTs and modifies the surface-active sites and the distribution of Lewis and Brønsted acid sites, as found elsewhere [ 59 ]. Meanwhile, a steep plateau in the NO x conversion is seen in CoNT catalyst with prolonged reaction time due to Co sites oxidation by water vapor.…”

Investigation of the Deactivation Behavior of MeMo/La2O3-Al2O3- and MeMo/Nb2O5 Supported Catalysts (Me = Pt, Ni, and Co) in Tri-Reforming of Methane

“…It is worth mentioning that PM/Nb is a sintering-resistant solid due to the strong metal–support appearing between Pt and the Nb–O–Mo support, and thus, the catalytic activity during TRM is maintained compared with NM/Nb and CM/Nb (Figure and Figure ). This can be evidenced from the fact that the well-dispersed Pt nanoparticles in close contact with Mo/Nb 2 O 5 split into PtO x and the other alloy between Mo and Pt . Moreover, the reasons for the superior catalytic activity of PM/Nb are not clear at this point, since catalytic performance is 1 to 2 orders of magnitude higher than that on the PM/LaAl catalyst.…”