Hydrotalcite-Modified Clinoptilolite as the Catalyst for Selective Catalytic Reduction of NO with Ammonia (NH3-SCR)

Abstract

A series of clinoptilolite-supported catalysts, modified with hydrotalcite-like phase (HT) by co-precipitation, were prepared and tested in NH3-SCR reactions. It was found that deposition of HT on clinoptilolite increased conversion of NO within 250–450 °C, and that the positive impact on the catalytic activity was independent of HT loading. The promoting effect of clinoptilolite was attributed to Brönsted acid sites present in the zeolite, which facilitated adsorption and accumulation of ammonia during the catalytic process. Concentration of N2O in the post-reaction gas mixture reached its maximum at 300 °C and the by-product was most likely formed as a consequence of NH4NO3 decomposition or side reaction of NH3 oxidation in the high-temperature region. The gradual elimination of nitrous oxide, noticed as the material with the highest concentration of hydrotalcite phase, was attributed to the abundance of oligomeric iron species and the superior textural parameters of the material. UV-Vis experiments performed on the calcined samples indicated that Fe sites of higher nuclearity were generated by thermal decomposition of the hydrotalcite phase during the catalytic reaction. Therefore, calcination of the materials prior to the catalytic tests was not required to obtain satisfactory overall catalytic performance in NO reductions.

Clinoptilolite—An Efficient Carrier for Catalytically Active Nano Oxide Particles

“…Various zeolites, such as BEA, FAU or ZSM, have been tested [94][95][96][97]. CLI has also been recognized as a suitable candidate for SCR using ammonia or hydrocarbons as reducing agents [98][99][100][101][102][103][104][105][106][107][108]. Even non-modified CLI possesses catalytical activity, which was ascribed to the presence of iron species, which are the main impurity in the zeolitic tuffs [98][99][100].…”

“…Recently, catalysts prepared through the coprecipitation of hydrotalcite (HT) on CLI were tested in the SCR reaction with ammonia [108]. The deposition of HT on the CLI resulted in a high conversion rate at 250-450 • C (95%).…”