Investigation of Various Pd Species in Pd/BEA for Cold Start Application

Abstract

A series of Pd/BEA catalysts with various Pd loadings were synthesized. Two active Pd2+ species, Z−-Pd2+-Z− and Z−-Pd(OH)+, on exchanged sites of zeolites, were identified by in situ FTIR using CO and NH3 respectively. Higher NOx storage capacity of Z−-Pd2+-Z− was demonstrated compared with that of Z−-Pd(OH)+, which was caused by the different resistance to H2O. Besides, lower Pd loading led to a sharp decline of Z−-Pd(OH)+, which was attributed to the ‘exchange preference’ for Z−-Pd2+-Z− in BEA. Based on this research, the atom utilization of Pd can be improved by decreasing Pd loading.

Effects of Treatment Conditions on Pd Speciation in CHA and Beta Zeolites for Passive NOx Adsorption

“…Initially, ceria–zirconia mixed oxides and various metal-doped aluminas were examined but were found to be poisoned by sulfates when sulfur is present in the exhaust gas . As a result, palladium-loaded zeolites were evaluated and showed the absence of NO x stored as nitrates in the presence of NO and thus also achieved more complete desorption of NO x under typical operating temperatures. − …”

Emissions Control Catalysis

“…Zhang et al [27] investigated the NO x storage capacity of a series of Pd/BEA catalysts with various Pd loadings for cold-start applications. In situ FTIR measurements using CO and NH 3 enable the authors to identify two isolated Pd 2+ species, Z − -Pd 2+ -Z − and Z − -Pd(OH) + , on exchanged sites of zeolites, as the main active sites for NO trapping.…”

“…The review of Smirniotis P. and co-workers [18] concerns the selective catalytic reduction of NO x with NH 3 (NH 3 -SCR of NO x ) focusing to low temperature applications that is a highly desirable perspective, and finally the review of Bogaerts A. and co-workers [19] covering a hot recent trend in emissions control implicating cyclic economy strategies, that is the conversion and utilization of CO 2 for the production of value-added chemicals. On the other hand, a major part of contributions (9/21) concerns original research on nitrogen oxides reduction processes [20][21][22][23][24][25][26][27][28], reflecting the fact that this topic still remains hot among the targets of environmental catalysis. Five out of 21 studies concern CO and hydrocarbons oxidation processes [29][30][31][32][33] while the remained 4/21 concern CO 2 capture/recycling processes under the view of cyclic economy [34][35][36][37].…”

Recent advances in catalytic automotive emission control: Passive NO storage at low temperatures

“…The performance of the Pd/zeolite catalysts strongly depends on the chemical state of Pd during the NO adsorption. [ 10,19,71 ] Based on the CO and NO‐DRIFTs results, Chen et al [ 10 ] proposed that Pd 2+ ions were the NO adsorption sites for NO adsorption as Pd 2+ (NO). However, for all the Pd/SSZ‐13, Pd/ZSM‐5, and Pd/Beta catalysts, the mole ratio of stored NO to Pd was lower than 1, which was ascribed to the formation of inert PdO in the Pd/zeolite catalysts.…”

“…One is the materials amorphous oxide (e.g., Al 2 O 3 , TiO 2 , or CeO 2 , or their solution solids) with noble metal (i.e., Pt, Pd, or Ag) loading, and the other is the Pd/zeolites (e.g., Pd/SSZ‐13, Pd/Beta, and Pd/ZSM‐5) catalysts. [ 8,12,14,16,18,19 ] Both kinds of catalysts show high NO adsorption capacity at low temperatures and the stored NO x can be released when the catalysts reached high temperatures. However, as a supplemental device for current SCR and NSR section in the after‐treatment system, PNA catalysts need to meet several strict requirements.…”