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Open AccessFeature PaperReview

Electropositive Promotion by Alkalis or Alkaline Earths of Pt-Group Metals in Emissions Control Catalysis: A Status Report

1
Laboratory of Physical Chemistry & Chemical Processes, School of Environmental Engineering, Technical University of Crete (TUC), 73100 Chania, Crete, Greece
2
Univ. Lyon, Université Claude Bernard Lyon 1, CNRS—IRCELYON—UMR 5256, 2 Avenue A. Einstein, 69626 Villeurbanne, France
*
Author to whom correspondence should be addressed.
Catalysts 2019, 9(2), 157; https://doi.org/10.3390/catal9020157
Received: 23 December 2018 / Revised: 25 January 2019 / Accepted: 29 January 2019 / Published: 5 February 2019
(This article belongs to the Special Issue Emissions Control Catalysis)
Recent studies have shown that the catalytic performance (activity and/or selectivity) of Pt-group metal (PGM) catalysts for the CO and hydrocarbons oxidation as well as for the (CO, HCs or H2)-SCR of NOx or N2O can be remarkably affected through surface-induced promotion by successful application of electropositive promoters, such as alkalis or alkaline earths. Two promotion methodologies were implemented for these studies: the Electrochemical Promotion of Catalysis (EPOC) and the Conventional Catalysts Promotion (CCP). Both methodologies were in general found to achieve similar results. Turnover rate enhancements by up to two orders of magnitude were typically achievable for the reduction of NOx by hydrocarbons or CO, in the presence or absence of oxygen. Subsequent improvements (ca. 30–60 additional percentage units) in selectivity towards N2 were also observed. Electropositively promoted PGMs were also found to be significantly more active for CO and hydrocarbons oxidations, either when these reactions occur simultaneously with deNOx reactions or not. The aforementioned direct (via surface) promotion was also found to act synergistically with support-mediated promotion (structural promotion); the latter is typically implemented in TWCs through the complex (Ce–La–Zr)-modified γ-Al2O3 washcoats used. These attractive findings prompt to the development of novel catalyst formulations for a more efficient and cost-effective control of the emissions of automotives and stationary combustion processes. In this report the literature findings in the relevant area are summarized, classified and discussed. The mechanism and the mode of action of the electropositive promoters are consistently interpreted with all the observed promoting phenomena, by means of indirect (kinetics) and direct (spectroscopic) evidences. View Full-Text
Keywords: platinum; palladium; Rhodium; iridium; NO; N2O; propene; CO; methane; alkali; alkaline earth; platinum group metals; deNOx chemistry; lean burn conditions; TWC; catalyst promotion; EPOC platinum; palladium; Rhodium; iridium; NO; N2O; propene; CO; methane; alkali; alkaline earth; platinum group metals; deNOx chemistry; lean burn conditions; TWC; catalyst promotion; EPOC
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Yentekakis, I.V.; Vernoux, P.; Goula, G.; Caravaca, A. Electropositive Promotion by Alkalis or Alkaline Earths of Pt-Group Metals in Emissions Control Catalysis: A Status Report. Catalysts 2019, 9, 157.

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