Structural Characterization and Selective Catalytic Reduction of Nitrogen Oxides with Ammonia: A Comparison between Co/ZSM-5 and Co/SBA-15

Abstract

Cobalt-containing catalysts supported on ZSM-5 zeolite and mesoporous siliceous SBA-15 were prepared and characterized by nitrogen sorption, X-ray diffraction, scanning electron and transmission electron microscopies, energydispersive X-ray, Fourier transform infrared, ultraviolet−visible diffuse reflectance, X-ray photoelectron spectroscopies, and temperature-programmed desorption of ammonia measurement. The effect of cobalt loading ratio on the selective catalytic reduction (SCR) of nitrogen oxides (NO x ) with ammonia was investigated. The existing Brønsted acid sites contributed to the cobalt species finely dispersed within the ZSM-5 zeolite, either as isolated cobalt ions anchored at α, β, and γ sites, or as amorphous cobalt oxides enriched on the ZSM-5 surface. NO x conversion profiles of Co/ZSM-5 exhibited two peaks. The low-temperature peak (<300 °C) was induced by cobalt ions at β and γ sites, while the high-temperature peak (>300 °C) was assigned to the amorphous and crystalline cobalt oxides. With increasing cobalt content, the intensity of lowtemperature peak was enhanced monotonously, and the peak position remained constant. Increasing cobalt content promoted the high-temperature peak to shift toward lower temperatures. NO x conversion profiles of Co/SBA-15 only exhibited a hightemperature peak. For Co/SBA-15, the poor dispersion of cobalt species was derived from the absence of Brønsted acid sites. The activity of Co/SBA-15 catalysts was lower than that of the Co/ZSM-5 catalysts due to inactive cobalt ions anchored on isolated Si−OH groups, and agglomerated cobalt oxides within the SBA-15 channels blocking the reactant pathway to active sites.

A preliminary evaluation of ZSM-5/SBA-15 composite supported Co catalysts for Fischer–Tropsch synthesis

“…4d). It can be speculated that most cobalt particles were likely to form on the external surface of ZSM-5, which was in accord with the SEM image and literature reports that the Co species were prone to migrate and aggregate on the surface of ZSM-5 after the incipient wetness impregnation process with higher cobalt content [35,43].…”

“…For Co/ZS-0, SBA-15 pores were clogged by cobalt species that made them inaccessible for nitrogen adsorption. Since the Co/ZSM-5 was prepared by incipient wetness impregnation and the cobalt content was 15wt.%, the chance for to enter into the micropores of ZSM-5 was usually low and CoO x was most likely to migrate and aggregate on the surface of ZSM-5 [34,35,43]. As a result, the cobalt species did not affect the nitrogen adsorption behaviour of ZSM-5.…”

Influence of Porosity on Product Distribution over Co/H‐ZSM‐22 Catalysts in the Upgrading of Palmitic Acid

“…The second peak (346 °C for Co/HZ‐22, 335 °C for Co/HZP‐22) and third peak (374 °C for Co/HZ‐22, 365 °C for Co/HZP‐22) were ascribed to Co 3 O 4 →CoO and CoO→Co 0 , respectively, as in the case of the Co/SiO 2 precursor (Figure a) . Furthermore, higher reduction temperatures were observed at around 435 and 553 °C especially for the Co/HZP‐22 precursor, which were attributed to the distribution of Co 2+ species over mesopores HZP‐22 and strong metal‐support interaction, respectively …”

Spatial Confinement Effects of Microcapsule Catalyst for Improved Coking‐ and Sintering‐Resistant Behaviors Toward CO2 Reforming of Methane Reaction

“…So far, efforts have been made to improve the coking‐ and sintering‐resistant abilities of Ni‐based catalysts . Studies show that small, evenly dispersed, and well supported nickel particles give the best catalytic activity . Capsule catalysts with a core/shell structure are proved to have these characteristics and are efficient for various reactions due to the spatial confinement effect .…”