Low-temperature SCR of NO_x with NH_3 over activated carbon fiber composite-supported metal oxides

摘要

In previous works, the authors were involved in the preparation and otpimization of Nomex-based activated carbon fibers (ACFs) monoliths and their use as catalytic supports of manganese oxides for the selective catalytic reduction(SCR) of NO_x with NH_3 at low temperature. Thus, a low density monolith made of carbonized Nomex~(TM) rejects was fabricated and submitted to different surface conditioning treatments in order to maximize the dispersion and loading of manganese oxides which were highly active in the SCR process. In order to complete the study, in this work different carbon fibers were used to fabricate the monolithic support, and the catalytic activity of the derived manganese oxide-based catalysts was analyzed and compared to that of the standard Nomex~(TM)-supported catalyst. THese fibers were coal Pitch-, Rayon-, PAN-, and phenolic Resin-based carbon fibers. Additionally, catalysts based on other metal oxides (nickel, chromium, vanadium and iron) were prepared via equilibium adsorption (EA) and pore volume impregnation (PVI) of the strategically modified supports, in an attempt to surpass the catalytic performance of the already highly active manganese oxide-based catalytsts and to tackle one of the main drawbacks for the utilization of these catalysts under practical ocnditions; the SO_2 deactivation. For all the prepared catalysts the following parameters were evaluated at a standard reaction temperature of 150 deg C: catalytic activity selectivity, extent of support gasification, H_2O inhibition and SO_2 deactivation. Additonally temperature programmed desorption (TPD) of NO was conducted on specific samples in order to analyze the different adsorption modes of NO on the catalytic surface. All this research procedure has eventually derived in the selection of a catalyst (Nomex~(TN) rejects-based activated carbon fiber composite (ACFC) supported iron oxides) which constitutes a compromise between high catalytic performance and moderate SO_2 deactivation.