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

• Main Authors: João Pedro S. Nascimento, Lais F. Oton, Alcineia C. Oliveira, Elena Rodríguez-Aguado, Enrique Rodríguez-Castellón, Rinaldo S. Araujo, Monique S. Souza, Rossano Lang
• Format: Article
• Language: English
• Published: MDPI AG 2020-09-01
• Series: Catalysts
• Subjects: Nb₂O₅; catalyst; synergistic effect; NO_x; CO-SCR
• Online Access: https://www.mdpi.com/2073-4344/10/9/1048
• ISSN: 2073-4344

Doubly promoted MeMo/Nb₂O₅ catalysts, in which Me = Pt, Ni, or Co oxides were prepared for the selective catalytic reduction of NO_x 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 NO_x and CO chemisorption was at low reaction temperatures, whereas the NO_x 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 PtO_x entrapped on MoO₃ sites induced high NO_x 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 NO_x conversions over NiMo and PtMo sites, whereas the structure of CoMo ones remained very active with a maximum NO_x 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.