Challenges and Solutions in Developing Zeolite Supported Transition Metal Catalysts for Lean-Burn NOx Emission Control

Meeting Program — September 2014

Hai-Ying Chen
Emis­sion Con­trol Tech­nolo­gies
John­son Matthey Inc.
Wayne, PA

Abstract — Reduc­tion of NOx emis­sions from lean-burn engine exhaust has been a main top­ic of envi­ron­men­tal catal­y­sis in the past 20 years. The chal­lenge is the selec­tive con­ver­sion of a low con­cen­tra­tion of NOx (~100 ppm) in the pres­ence of large excess of O2 (~10%). Although zeo­lite sup­port­ed tran­si­tion met­al cat­a­lysts were iden­ti­fied in ear­ly 1990s as promis­ing cat­a­lysts, such a tech­nol­o­gy was not imple­ment­ed till recent­ly.

Ear­ly stud­ies main­ly focused on the devel­op­ment of zeo­lite sup­port­ed tran­si­tion met­al, pri­mar­i­ly Cu and Fe, cat­a­lysts for the selec­tive cat­alyt­ic reduc­tion of NOx with hydro­car­bons (HC-SCR). Even though the HC-SCR tech­nol­o­gy has been con­sid­ered as the “holy grail” of auto­mo­tive catal­y­sis, tech­ni­cal chal­lenges on the activ­i­ty, selec­tive and dura­bil­i­ty of the cat­a­lysts were rec­og­nized to be dif­fi­cult to over­come for the tech­nol­o­gy to be imple­ment­ed into real world appli­ca­tions. How­ev­er, the vast amount of research work, espe­cial­ly the fun­da­men­tal stud­ies on the reac­tion and the cat­a­lyst deac­ti­va­tion mech­a­nisms, demon­strat­ed that the activ­i­ty and selec­tiv­i­ty of this type of cat­a­lysts can be dras­ti­cal­ly improved if an alter­na­tive reduc­tant, NH3, is avail­able in the feed.

Exten­sive inves­ti­ga­tions on the selec­tive cat­alyt­ic reduc­tion of NOx with NH3 (NH3-SCR) began in the mid­dle 2000s aimed to enable diesel pow­ered vehi­cles to meet the US EPA 2007/2010 emis­sion reg­u­la­tions. Both Cu and Fe cat­a­lysts were con­sid­ered. Zeo­lite sup­port­ed Cu SCR cat­a­lysts are more active at low tem­per­a­ture, thus more attrac­tive for appli­ca­tions with low exhaust tem­per­a­ture. The con­ven­tion­al medi­um-pore zeo­lite (10-ring, such as ZSM-5) or large-pore zeo­lite (12-ring, such as beta) sup­port­ed Cu cat­a­lysts, how­ev­er, can­not meet the long-term dura­bil­i­ty require­ments. To over­come this major tech­ni­cal hur­dle, small-pore zeo­lite (8-ring) sup­port­ed Cu cat­a­lysts were invent­ed. On the oth­er hand, zeo­lite sup­port­ed Fe SCR cat­a­lysts are more selec­tive in uti­liz­ing NH3 for NOx reduc­tion at high tem­per­a­tures but show a strong depen­dence on the NO to NO2 ratio in the feed gas at low tem­per­a­tures. Sys­tem approach­es were devel­oped to enhance the low tem­per­a­ture SCR activ­i­ty of the Fe SCR cat­a­lysts. As such, both Cu and Fe SCR cat­a­lysts were suc­cess­ful­ly com­mer­cial­ized and applied on lean-burn diesel vehi­cles meet­ing the strin­gent US EPA 2010 emis­sion stan­dards.

Hai-Ying ChenBiog­ra­phy — Dr. Hai-Ying Chen is a Sci­en­tif­ic and Prod­uct Devel­op­ment Man­ag­er at John­son Matthey, where he leads a team of sci­en­tists to devel­op advanced emis­sion con­trol cat­a­lysts and tech­nolo­gies for both gaso­line engine and diesel engine pow­ered vehi­cles to meet the gov­ern­ment emis­sion reg­u­la­tions.

Dr. Chen received his Ph.D. in Chem­istry from Fudan Uni­ver­si­ty, Chi­na. He has pub­lished more than 50 tech­ni­cal papers in peer-reviewed jour­nals and holds 14 US/international patents. He received the Top Cit­ed Arti­cle Award by Catal­y­sis Today for arti­cles pub­lished in 1998, and was a recip­i­ent of the Amer­i­can Chem­i­cal Soci­ety Award for Team Inno­va­tion in 2009. He was named as the 2014 Her­man Pines Award in Catal­y­sis by the Chica­go Catal­y­sis Club and the 2014 Catal­y­sis Club of Philadel­phia Award by the Catal­y­sis Club of Philadel­phia.