Passive in situ generation of additional reductant intermediates for the assisted green hydrogen engines NOx removal – H-toClean

The implementation of batteries or fuel cells as a decarbonised propulsion method for heavy trucks remains an issue for cost and energy density reasons. One alternative solution lies in the development of green hydrogen internal combustion engines (H2-ICEs), as studied by Renault Trucks (which express high interest in the project). This purpose benefits from their expertise in the field of ICEs. Nevertheless, traces of NOX may persist during lean-burn combustion of H2. Traditional three-way catalysts (TWC) are not suitable for lean mixture treatment and the current Diesel deNOX treatment using urea (NH3-SCR) is technically constraining, costly and leads to CO2 emission. The most attractive approach is the NOx selective catalytic reduction by unburned H2 (H2-SCR). Unfortunately, to date, catalysts proposed for this process suffer from a narrow activity temperature range and a lack of selectivity, not suitable with the targeted application.
The H-to-Clean project proposes the development of tailored catalysts for the H2-SCR based on the oxidation–reduction mechanism: N2 is then obtained via reactions between gaseous NO or weakly adsorbed oxidized species (NO–, NO2–, NO3–) and adsorbed reduced N compounds (NHX). For the NHX species formation, Fe and Ru are of great interest and the successive coordination or protonation of NHx species is promoted by Lewis or Brønsted acid sites, respectively. Basic sites are also involved via the formation of adsorbed nitrosonium/nitrate to finally produce the NHx-NOx key intermediate species. Our preliminary results have confirmed the potential of this approach. The H-to-clean consortium aims to develop multi-functional catalysts combining active sites for hydrogenation (Fe, Ru), acid functions to favour the NHx formation and to promote the decomposition rate of nitrosamine intermediates, and basic sites for the nitrosonium/nitrate formation. In addition, the H-to Clean project will explore a prospect complementary task with the in situ generation of C-containing reduced intermediates species as active reductant agent for NOX reduction, through the promotion of formate or CHx species obtained from the CO2 present in the combustion air.
To achieve this project successfully, two academic partners recognized in the concerned fields are involved: IC2MP (Institut de Chimie des Milieux et Matériaux de Poitiers) and IRCELYON (Institut de Recherches sur la Catalyse et l’Environnement de Lyon).
In addition to the “project management” work package (WP), the project methodology is based on five interconnected WPs. WP1 and WP2 are dedicated to the preparation of two catalysts families: metal supported acid-based oxides (IC2MP) and exsolved-metal supported on perovskites (IRCELYON). To gain efficiency in the catalysts developments, each laboratory will perform usual characterizations and deNOx catalytic tests in realistic conditions (WP3). To describe the involved surface properties and catalytic mechanism of the most promising catalysts, advanced characterizations will be share and combined between the two Laboratories (WP4). IC2MP will focus on dynamic transient experiments and Temperature Programmed Surface Reaction (TPSR) while IRCELYON will implement advanced in situ characterizations (spectroscopy, microscopy and XRD). WP5 also concerns a transversal work package, devoted to the generation of C-containing reduced intermediate species. IRCELYON will study the surface CHx promotion while the C-intermediates will be evaluated in hydrogen assisted CHx-SCR experiments at IC2MP using formaldehyde (H-CHO) and formic acid (H-COOH) for instance. Finally, combinations of materials in a dual catalytic bed system, possibly involving the two proposed routes (C and N-reduced intermediates), could contribute to achieve the challenging outcome dealing with the development of active, in a wide temperature range, and selective catalytic NOx converters for H2-ICEs.