Al2O3-based passive NOx adsorbers for low temperature applications

Abstract

NOx storage on Pt/Al 2 O 3 and Pt/La-Al 2 O 3 in the temperature range 80-160 ºC was investigated by means of microreactor and in situ DRIFTS experiments, to ascertain their suitability for

Achieving Atomic Dispersion of Highly Loaded Transition Metals in Small‐Pore Zeolite SSZ‐13: High‐Capacity and High‐Efficiency Low‐Temperature CO and Passive NOx Adsorbers

“…[11,50] In summary,w ep rovide ad irect, simple,a nd scalable route to highly loaded ionic Pd and Pt in asmall-pore siliceous (3 < Si/Al < 12) zeolite.This route utilizes only wet chemistry and does not require the use of expensive organometallic precursors or organic solvents.The key is to use the NH 4 -form of the zeolite and the modified IWI method, not the conventional ion exchange.F urthermore,w er econcile the contradictory literature data which the FTIR characterization for high loaded Pt and Pd species in ZSM-5 and other zeolites Angewandte Chemie Zuschriften always indicates the presence of significant amounts of metallic nanoparticles (not well-dispersed Pd or Pt) because: 1) H-forms of zeolite are often used for ion exchange,2)Si/Al ratios > 10 are not able to disperse metals as individual atoms because of the decreased hydrophilicity of the zeolite micropores 3) ForP t, the calcination temperature should not exceed 350 8 8Cb ecause of the instability of ionic Pt 2+ above this temperature.T his new insight led to the synthesis of Pd/ SSZ-13 with up to 2wt% of atomically dispersed Pd for immediate industrial application as CO and passive NO x adsorbers.T hese materials are able to abate 180 mmole g À1 NO x and simultaneously CO during cold-start of the vehicle while maintaining atomic dispersion. We achieved complete utilization of each Pd atom, surpassing the best performance of Pd/zeolite adsorbers reported in both patent [38,39] and open [35][36][37][40][41][42][43][44][45] literature.…”

“…Calcination at 400 8 8C, however, resulted in the formation of metallic Pt nanoparticles on the external surface of the zeolite crystals ( Figure S15): ionic Pt in SSZ-13 is unstable at temperatures > 400 8 8C, even when O 2 is present in the gas-phase and thermal treatment leads to the formation of metallic Pt particles.F TIR spectra of adsorbed CO on the 400 8 8Ccalcined 1wt% Pt/SSZ-13 showed ap rominent feature approximately 2090 cm À1 ,c onfirming the formation of metallic Pt clusters ( Figure S16). We achieved complete utilization of each Pd atom, surpassing the best performance of Pd/zeolite adsorbers reported in both patent [38,39] and open [35][36][37][40][41][42][43][44][45] literature. We achieved complete utilization of each Pd atom, surpassing the best performance of Pd/zeolite adsorbers reported in both patent [38,39] and open [35][36][37][40][41][42][43][44][45] literature.…”

“…[35][36][37][38][39][40][41][42][43][44][45][46] This is the major source of NO x pollution in the world and it affects public health and atmospheric chemistry.W eh ave shown that Pd-loaded zeolites were able to store NO x at low temperatures as NO + and Pd I/II -NO nitrosyl complexes. [35][36][37][38][39][40][41][42][43][44][45][46] This is the major source of NO x pollution in the world and it affects public health and atmospheric chemistry.W eh ave shown that Pd-loaded zeolites were able to store NO x at low temperatures as NO + and Pd I/II -NO nitrosyl complexes.…”

“…Most NO x emissions from internal combustion engines occur during cold-start when the SCR catalyst is still inactive. [35][36][37][38][39][40][41][42][43][44][45][46] This is the major source of NO x pollution in the world and it affects public health and atmospheric chemistry.W eh ave shown that Pd-loaded zeolites were able to store NO x at low temperatures as NO + and Pd I/II -NO nitrosyl complexes. However,i nt he engine exhaust gas mixture H 2 Oi sa lways present in significant amounts:H 2 Ocompetes for Pd sites and blocks NO adsorption.…”

Excited-State Dynamics in Colloidal Semiconductor Nanocrystals

“…Methods to reduce blinking of NCs (i.e., to make random switches to a dark state less frequent) include surface protection using organic ligands [281] or an inorganic shell material [195,282,283], and also plasmonic enhancement of radiative decay [284]. This indicates that blinking involves slow changes on the surface of the QD that introduce non-radiative decay pathways.…”