Palladium doped perovskite-based NO oxidation catalysts: The role of Pd and B-sites for NOx adsorption behavior via in-situ spectroscopy

Abstract

a b s t r a c tPerovskite-based materials (LaMnO 3 , Pd/LaMnO 3 , LaCoO 3 and Pd/LaCoO 3 ) were synthesized, characterized (via BET, XRD, Raman spectroscopy, XPS and TEM) and their NO x (x = 1,2) adsorption characteristics were investigated (via in-situ FTIR and TPD) as a function of the nature of the B-site cation (i.e. Mn vs Co), Pd/PdO incorporation and H 2 -pretreatment. NO x adsorption on of LaMnO 3 was found to be significantly higher than LaCoO 3 , in line with the higher SSA of LaMnO 3 . Incorporation of PdO nanoparticles with an average diameter of ca. 4 nm did not have a significant effect on the amount of NO 2 adsorbed on fresh LaMnO 3 and LaCoO 3 . TPD experiments suggested that saturation of fresh LaMnO 3 , Pd/LaMnO 3 , LaCoO 3 and Pd/LaCoO 3 with NO 2 at 323 K resulted in the desorption of NO 2 , NO, N 2 O and N 2 (without O 2 ) below 700 K, while above 700 K, NO x desorption was predominantly in the form of NO + O 2 . Perovskite materials were found to be capable of activating N-O linkages typically at ca. 550 K (even in the absence of an external reducing agent) forming N 2 and N 2 O as direct NO x decomposition products. H 2 -pretreatment yielded a drastic boost in the NO oxidation and NO x adsorption of all samples, particularly for the Cobased systems. Presence of Pd further boosted the NO x uptake upon H 2 -pretreatment. Increase in the NO x adsorption of H 2 -pretreated LaCoO 3 and Pd/LaCoO 3 surfaces could be associated with the electronic changes (i.e. reduction of B-site cation), structural changes (surface reconstruction and SSA increase), reduction of the precious metal oxide (PdO) into metallic species (Pd), and the generation of oxygen defects on the perovskite. Mn-based systems were more resilient toward B-site reduction. Pd-addition suppressed the B-site reduction and preserved the ABO 3 perovskite structure.

DFT Analysis of NO Oxidation Intermediates on Undoped and Doped LaCoO3 Perovskite

“…Say et al 20 used vibrational spectroscopy to observe features attributed to adsorbed nitrite and nitrate at 323K after saturating the surface with 5 Torr NO 2 for 10 minutes.…”

Catalytic combustion of toluene with Pd/La0.8Ce0.2MnO3 supported on different zeolites

“…As shown in the Table 1 increased, when they were doped with Pd, the increase of the surface area was observed, which was very likely indication that a more uniform coating of Pd [17]. It was also found that b-zeolite and ZSM-5 exhibited larger mesopore volume, the mesopore volume of b-zeolite and ZSM-5 were 0.075 and 0.053 cm 3 /g, respectively.…”

“…This result indicated that the Pd species were highly dispersed on the surface of the carrier. The main reason was likely the small particle size, low volume percentile, or lack of crystallographic order in such phase [17,20].…”

Síntese e caracterização de perovskitas LaMnO3 e γ-alumina como catalisadores para a reação de combustão do metano

“…Dentre os catalisadores conhecidos, destacam-se os materiais a base de metais nobres, como o paládio [8]. Entretanto, devido ao seu custo elevado, materiais ativos e mais econômicos têm sido propostos como alternativa ao uso destes metais [9,10].…”

“…Estudos indicam que catalisadores a base de óxidos mistos, como as perovskitas, apresentam-se ativos e termoestáveis quando aplicadas a combustão do metano [9,10].…”