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Application of the concepts of electromechanical promotion- NEMCA - and carrier doping - DIMSI - in designing novel de-NOx catalysts for lean-burn engines

Objective


New bipolar configurations of Rh/YSZ film catalyst of low current bypass were realised; for the first time a new bipolar configuration of 2nd generation (catalyst film in a monolith YSZ reactor with multiple channels) was realised by deposition of a RuO2 catalyst film which under model test conditions resulted in a 50% increase in the conversion at high open circuit conversion (35%);
- An YSZ tube (length: 10 cm, ID: 3/4 in) with the outer area coated with two gold electrodes and the inner area totally covered by an Rh thin film deposited by sputtering at room temperature was tested in both laboratory and test rig apparatus. Significant enhancements in catalytic activity were shown in laboratory experiments, while no significant enhancement of the catalyst performance were found in test rig experiments due to high flow rates and presence of bypass phenomena;
- Effectiveness of both anodic and cathodic polarization was demonstrated in presence of O2; in NO conversion by propene/O2 enhancement factors of up to 2.5 with good N2 selectivity (50-90% range) were obtained both in CSTR and in tubular reactor type experiments;
- Current application with insignificant power consumption was shown to efficiently assist the recovery of lost catalytic activity of Rh/YSZ film catalysts with respect to reduction of NO by propylene in excess oxygen conditions by increasing the reduction rate of oxidized surface sites via weakening the rhodium-oxygen bond;
- The applicability of the NEMCA effect was shown to be present for the first time in the presence of O2 in the feed. The promotional effect caused by NEMCA was more pronounced in feeds containing small O2 concentrations;
- Rh films promoted with Na were shown to have significantly higher activity as compared to the unpromoted open circuit performance of the same Rh film, indicating for the first time the synergetic effect of Chemical and Electrochemical Promotion;
- Methods for the deposition of robust electrodes on pelletized dispersed metal catalysts supported on solid electrolytes have been developed and techniques for the preparation of pellets made of highly dispersed catalysts on YSZ, TiO2(D) and CeO2(D) with two terminal electrodes were developed;
- Catalysts modified by DIMSI effect (doped Rh/TiO2 and Rh/ZrO2) were shown to have superior selectivity characteristics in the reduction of NO by C3H6/O2 in the presence of H2O and SO2 in the feed and to SO2 resistant; the metal/dopant ratio was demonstrated as a critical parameter controlling the performance of the DIMSI-modified catalysts examined under realistic conditions;
- Catalysts based on Pt/TiO2-Al2O3 were shown to combine a high selectivity in the reduction of NO to N2 and a wider range of reaction temperatures of maximum conversion of NO.
Objectives and content
The objective of this project is to develop selectively
acting N0x catalysts in the presence of oxygen for auto
exhaust after treatment. Although efficient catalytic
devices exist today for reducing N0x for stoichiometric
operated gasoline engines, no such devises are available
for lean burn and diesel engines. The need for such
catalysts is great, taking into consideration the fact
that lean burn engines offer considerable, up to 15%,
enhancement in fuel efficiency and that nitrogen oxides
released to the environment cause severe environmental
damage which is related to smog formation and acid rain.
The proposed investigation will lead to the development
of innovative catalysts for the reduction of N0x with
hydrocarbons or C0 in the presence of excess oxygen.
The development of the novel catalytic materials is based
on the concepts of non-faradaic electrochemical
modification of catalytic activity (NEMCA) and dopantinduced metal-support interactions (DIMSI). These
phenomena are used to alter the surface potential and
work function of catalytic surfaces which, in turn,
alters significantly their chemisorptive and catalytic
parameters in the desired direction.
In the case of NEMCA or electrochemical promotion, the
catalyst, in the form of a porous polycrystalline film,
is supported on a solid electrolyte support, such as
Y203-stabilized ZrO2 (YSZ), an o2 conductor, b"-AI203 or
Nasicon, Na+ conductors, and others. By applying
electrical current or potential (i2V) between the
catalyst and a counter electrode one can induce dramatic
and reversible changes in catalytic activity and
selectivity.
The phenomenon of DIMSI refers to alterations of the
chemisorptive and catalytic properties of small metal
crystallites dispersed on semiconductive carriers such as
Ti0X doped with altervalent cations. Doping of the
semiconductive carrier alters its electronic structure in
a desired direction, depending on the valence and the
concentration of the doping cations. As a result of an
electronic interaction developing at the carrier-metal
interface, the work function of surface metal atoms is
changed, which, hl turn, results in significant changes
in chemisorptive and catalytic properties.
The catalytic systems upon which the NEMCA and DIMSI
states will be induced and investigated under condition
of N0X reduction are those of Rah, Pt and Pd in model
catalysts consisting of metal films on YSZ, and supported
metals, highly dispersed on YSZ, TiO2 and CeO2 doped with
altervalent cations. The development of novel catalytic
materials will be supported by fundamental investigations
of the NEMCA and DIMSI states of the catalysts and their
effects on intrinsic chemisorptive and kinetic parameters
as well as on sulfur-resistance and hydrothermal
stability. A number of advanced characterisation and
probing techniques will be employed in the fundamental
studies, which include FT-IR under reaction conditions
and of suitable probe molecules, W-Vis-NIR diffuse
reflectance spectroscopy, temperature programmed (TPD,
TP0, TPR, TPSR) and isotopic labelling (SSITKA)
techniques, XPS, measurement of work function and of heat
of adsorption.
Promising catalysts will be tested in bench scale units
using gas mixtures resembling those of lean burn and
diesel engines. Detailed kinetic studies will also be
conducted, as well as durability studies with particular
emphasis to sulfur tolerance and hydrothermal stability.
Successful catalysts will undergo long-term durability
tests in a diesel engine using fuels with sulfur content
from 30 to 500 ppm. The consortium involves 5
academic and 2 industrial partners. The presence of a
catalyst manufacturer and an automobile manufacturer in
the consortium ensures efficient implementation of the
technology which will be developed.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

University of Patras
Address

26500 Patras
Greece

Participants (5)

Ecole Polytechnique Fédérale de Lausanne
Switzerland
Address

1015 Lausanne
JOHNSON MATTHEY PLC (TRADING AS SYNETIX)
United Kingdom
Address
Blounts Court, Sonning Common
RG4 9NH Reading
UNIVERSITA DEGLI STUDI DI MESSINA
Italy
Address
1,Salita Sperone 31
98166 Santagata Messina
University of Cambridge
United Kingdom
Address
Lensfield Road
CB2 1EW Cambridge
Volkswagen AG
Germany
Address

38440 Wolfsburg