Ammonia Abatement via Selective Oxidation over Electron-Deficient Copper Catalysts

Abstract

Selective catalytic ammonia-to-dinitrogen oxidation (NH 3 -SCO) is highly promising for the abatement of NH 3 emissions from flue gas purification devices. However, there is still a lack of high-performance and cost-effective NH 3 -SCO catalysts for real applications. Here, highly dispersed, electrondeficient Cu-based catalysts were fabricated using nitrogen-doped carbon nanotubes (NCNT) as support. In NH 3 -SCO catalysis, the Cu/NCNT outperformed Cu supported on N-free CNTs (Cu/ OCNT) and on other types of supports (i.e., activated carbon, Al 2 O 3 , and zeolite) in terms of activity, selectivity to the desired product N 2 , and H 2 O resistance. Besides, Cu/NCNT demonstrated a better structural stability against oxidation and a higher NH 3 storage capacity (in the presence of H 2 O vapor) than Cu/OCNT. Quasi in situ X-ray photoelectron spectroscopy revealed that the surface N species facilitated electron transfer from Cu to the NCNT support, resulting in electron-deficient Cu catalysts with superior redox properties, which are essential for NH 3 -SCO catalysis. By temperature-programmed surface reaction studies and systematic kinetic measurements, we unveiled that the NH 3 -SCO reaction over Cu/NCNT proceeded via the internal selective catalytic reaction (i-SCR) route; i.e., NH 3 was oxidized first to NO, which then reacted with NH 3 and O 2 to form N 2 and H 2 O. This study paves a new route for the design of highly active, H 2 O-tolerant, and low-cost Cu catalysts for the abatement of slip NH 3 from stationary emissions via selective oxidation to N 2 .

Economical and Sustainable Synthesis of Small-Pore Chabazite Catalysts for NOx Abatement by Recycling Organic Structure-Directing Agents

“…In addition, fewer N 2 O and NO 2 byproducts were generated over Cu-SSZ-13-R1 than Cu-SSZ-13-R0 (Figure S14c,d), which is likely due to inhibited NH 3 oxidation as a side-reaction. − The superior NH 3 -SCR performance of Cu-SSZ-13-R1 was maintained even in the presence of a higher H 2 O concentration of 8 vol % (Figure S14e,f) and showed no decay of NO conversion in a 24 h stability test at 200 °C (with 3 vol % H 2 O; see Figure S15). For both catalysts, the effect of hydrothermal aging (at 750 °C for 20 h) was rather mild, and NO conversions above 80% could be achieved in a broad temperature range from 200 to 375 °C (Figure d).…”

Revealing the Formation and Reactivity of Cage-Confined Cu Pairs in Catalytic NOx Reduction over Cu-SSZ-13 Zeolites by In Situ UV–Vis Spectroscopy and Time-Dependent DFT Calculation

“…Copper (Cu) ions confined in small-pore zeolites (CHA, LTA, AEI, etc. ) are highly active in ammonia-assisted selective catalytic reduction (NH 3 -SCR) of harmful nitrogen oxides (NO x ) and in catalytic partial oxidation of methane to methanol. − Notably, Cu-CHA (including Cu-SSZ-13 and Cu-SAPO-34) zeolites as NH 3 -SCR catalysts have been successfully deployed in commercial aftertreatment systems to remove NO x emissions from diesel exhausts. , Enormous research efforts have been put on the working mechanism of the Cu-CHA catalyst since its commercialization at around 2008–2009 and have significantly expanded our understanding of both NH 3 -SCR chemistry and Cu-zeolite catalysis. − Specifically, integration of in situ or operando spectroscopy, advanced simulations, and reaction kinetics allows revealing that the truly active Cu sites in Cu-CHA catalysts are mainly present as isolated Cu II and Cu II (OH), which are located in six-membered rings (6MRs) with two framework Al centers (2Al) and in eight-membered rings (8MRs) with one framework Al center (1Al), respectively. , During the standard NH 3 -SCR reaction ( i.e. , 4NH 3 + 4NO + O 2 → 4N 2 + 6H 2 O), the isolated Cu II and Cu II (OH) ions can be reduced by coadsorbed NH 3 and NO to monovalent Cu I moieties, which can be reoxidized to divalent Cu by NO and O 2 .…”

Review of the Catalytic System, Synthetic Process, and Support Morphological Research in Selective Catalytic Oxidation of Ammonia

“…In the selective catalytic oxidation of ammonia, the CuO@SAPO-34 catalyst outperformed bulk copper oxides made by the initial wet impregnation (IW) and Cu 2+ ion exchange techniques. Peng et al 181 prepared an efficient Cu-based NH 3 -SCO catalyst loaded on NCNT by a two-step vapor phase synthesis, including the oxidation in HNO 3 vapor. The activity of the NCNT-laden Cu catalysts (Cu/NCNT) was noticeably higher than that of the Cu catalysts that had been loaded with activated carbon (AC), nitrogen-free CNT, Al 2 O 3 , and ZSM-5 zeolites.…”