Fe Speciation in Iron Modified Natural Zeolites as Sustainable Environmental Catalysts

Abstract

Natural purified mordenite from Palmarito de Cauto (ZP) deposit, Cuba, was subjected to a hydrothermal ion exchange process in acid medium with Fe2+ or Fe3+ salts (Fe2+ZP and Fe3+ZP). The set of samples was characterized regarding their textural properties, morphology, and crystallinity, and tested in the NO reduction with CO/C3H6. Infrared spectroscopy coupled with NO as a probe molecule was used to give a qualitative description of the Fe species’ nature and distribution. The exchange process caused an increase in the iron loading of the samples and a redistribution, resulting in more dispersed Fe2+ and Fe3+ species. When contacted with the NO probe, Fe2+ZP showed the highest intensity of nitrosyl bands, assigned to NO adducts on isolated/highly dispersed Fe2+/Fe3+ extra-framework sites and FexOy clusters. This sample is also characterized by the highest NO sorption capacity and activity in NO reduction. Fe3+ZP showed a higher intensity of nitrosonium (NO+) species, without a correlation to NO storage and conversion, pointing to the reactivity of small FexOy aggregates in providing oxygen atoms for the NO to NO+ reaction. The same sites are proposed to be responsible for the higher production of CO2 observed on this sample, and thus to be detrimental to the activity in NO SCR.

Selective Catalytic Reduction of NOx by CO over Doubly Promoted MeMo/Nb2O5 Catalysts (Me = Pt, Ni, or Co)

“…The future development of the technologies for the abatement of gases from combustion of fossil fuels and diesel engines will require efficient routes for the conversion of these polluting gases into useful chemicals [1][2][3]. In this respect, selective catalytic reduction of hydrocarbons (SCR) has been recently claimed to be an extremely promising technology to eliminate exhaust gases [1,4]. This approach results in the reduction of the gases' release into the atmosphere, especially nitrogen oxides (NO x ), carbon oxides (CO x ), particulate matter (PM), volatile organic compounds (VOC) and sulfur oxides (SO x ) emissions [5][6][7].…”

Sustainable and Environmental Catalysis

“…The set of samples was characterized regarding their textural properties, morphology, and crystallinity, and tested in the NO reduction with CO/C 3 H 6 . The activity in hydrocarbons-selective catalytic reduction (HC-SCR) (used as a reaction test) was found to depend on the ion exchange process [15].…”

Low-Temperature Selective Catalytic Reduction of NO with NH3 over Natural Iron Ore Catalyst

“…Vanadium-based catalysts (V 2 O 5 /TiO 2 or V 2 O 5 -WO 3 /TiO 2 ) are the most common industrial catalysts for SCR of NO x with NH 3 , for which the most efficient reaction temperature range is 300~400 • C [4]. Since the operating temperature range is high, that is why the catalyst must be placed upstream of the desulfurizing section and the particulate removal device, to avoid reheating the flue gas; but it can cause deactivation due to the high concentration of sulfur dioxide and dust [5]. Other issues include high activity for the oxidation of SO 2 to SO 3 [6], the formation of N 2 O at high temperatures [7] and the toxicity of vanadium to the environment [8].…”