Au-based multimetallic nanoparticles embedded in zeolite nanoboxes for NO direct decomposition in excess O2 – DECOMPNOx

The ever more stringent legislations on vehicle emissions and the recent widely-reported revelations on the shortfalls of current technologies used for internal combustion engines impose the need for a step-change in emission control systems. The objective of the project is to design and evaluate new Au-based alloy nanoparticle catalysts for the direct decomposition of NOx (2 NOx = N2 + x/2 O2) in the presence of excess O2, thereby requiring no reductants.
This project could therefore bring a major advance in the use of lean-burn gasoline and diesel engine, which could lead to (i) fuel savings and less CO2 emissions, (ii) decreasing pollutants such as NOx, CO and soot (by allowing continuous and harsher oxidizing conditions), as well as (iii) major scientific advances in the understanding of the stability and reactivity of alloy nanoparticles for the dissociation of NO.
NO decomposition has been studied over many catalysts but none has reached commercial application so far. Metal-based formulations were shown to deactivate rapidly in the absence of reductant due to the poisoning presence of oxygen atoms strongly bound to the metal surface resulting from NO decomposition and O2 dissociation.
The first innovation brought about by the present project is to prepare multimetallic nanoparticles based on a highly reducible metal (Au) and metals active for NO decomposition in the 200-500°C temperature range. These Au-based formulations are expected to show a better resistance against oxygen poisoning or metal full oxidation because of the low stability of gold oxides. Combination of Pt, Pd, Ag, Cu and Rh with Au will be considered, since these metals are active for NO decomposition.
The second innovation will be to disperse these nanoparticles in basic zeolite hollow boxes that will (i) limit metal nanoparticle sintering and (ii) provide basic sites favoring NOx adsorption as nitrites and nitrates. The latter function could be crucial, if the adsorption of NOx appears to be rate-limiting on the metal nanoparticles. These NOx(ads) species are expected to be able to desorb or spill over onto the metal surface, as in traditional basic zeolites and NOx-Storage-Reduction materials. The basicity of the zeolite will be tuned by the addition of alkali or alkaline earth cations.
A set of about 20 samples of bi- and multimetallic nanoparticles encapsulated in zeolite multi-hollow nanoboxes will be prepared according to a novel synthesis method derived from that developed at IRCELYON for the preparation of alloys encapsulated in single hollow zeolite nanoboxes. LRS will investigate the catalytic activity for NO decomposition of the novel nanoalloy-based catalysts under experimental conditions representative of those of the exhausts of diesel or lean-burn engines, i.e. with NO, O2, CO2, H2O and SOx.
The strength of our approach is that, alongside traditional kinetic parameters obtained through effluent gas analyses, the adsorption and reaction of NOx will be determined by in situ and operando methods under realistic conditions (presence of O2, CO2, H2O, SOx at relevant temperatures).
The societal potential impact would be highly significant in terms of NOx and CO2 pollutant reductions in car exhaust gases, highly publicized lately in all media worldwide (particularly since the so-called Volkswagen scandal). Electric-powered vehicles will not be able to completely replace internal combustion engines before several decades and therefore more efficient catalytic converter are needed in the transition period for Diesel and lean-burn engines, which intrinsically produce less CO2 than gasoline engines.
If successful for mobile applications, the system should also be considered for the case of stationary sources, which currently rely on NH3-SCR or selective non-catalytic reductions (SNCR).