In situ Infrared Spectroscopic Studies on the Mechanism of the Selective Catalytic Reduction of NO by C₃H₈ over Ga₂O₃/Al₂O₃:  High Efficiency of the Reducing Agent

Abstract

The partial oxidation of propane and the mechanism of selective catalytic reduction (SCR) of NO by propane over Ga2O3/Al2O3 in excess of O2 have been investigated using in situ Fourier transform infrared spectroscopy. An optimized Ga2O3/Al2O3 catalyst shows high activity and efficiency of the reducing agent propane (100% conversion of NO at 623 K, GHSV: 10,000 h(-1)). One molecule of propane converts more than 4 NO molecules to N2. The reaction starts with the partial oxidation of C3H8 by O2 and carboxylates (acetate, formate) are formed on the catalyst surface above 573 K. This oxidation represents the rate-determining step of the SCR reaction. These surface carboxylates represent a dominating intermediate and (easily) react with (adsorbed) NO forming nitrogen-containing organic species. The latter are proposed to react with NO to form N2. Total oxidation of propane was enhanced at temperatures above 773 K leading to decreased reductant efficiency. Surface nitrite and nitrate species can also be observed, but they were found to be spectators only. This could be concluded from the electron balance (conversion of propane relative to NO) and from the relative rates of the single reaction steps. On the basis of these investigations and stoichiometric calculations, a conclusive reaction mechanism is proposed.

Promoting Effect of CeO2 on NO x Reduction with Propene over SnO2/Al2O3 Catalyst Studied with In situ FT-IR Spectroscopy

“…With increasing reaction temperature, the intensities of acrolein and acrylate decreased, while those bands at 1376, 1392, 1590 and 1462 cm -1 increased. The bands at 1376, 1392 and 1590 cm -1 can be assigned to the m s (COO -), d(CH) and m as (COO -) of adsorbed formate species, respectively [28,[31][32][33]. The band at 1462 cm -1 is attributed to the m s (COO -) of adsorbed acetate species [31,34].…”

ONIOM study of Ga/SAPO-11 catalyst: Species formation and reactivity

“…Due to their good Lewis acidity, Ga catalysts have found application in the aldol-type reactions of silyl enol ethers with carbonyl compounds [2]. Gamodified and Ga-exchanged zeolites have also been used for the alkylation of aromatic compounds [3], cycloalkane conversion [4], propane aromatization [5,6], selective catalytic NO reduction [7,8] More recently, the Ga/SAPO-11 system has been used for the direct transformation of n-butane to butenes [9].…”

In Situ FT-IR Studies on the Mechanism of Selective Catalytic Reduction of NOx by Propene over SnO2/Al2O3 Catalyst

“…using in situ FT-IR experiment and based on their findings some reaction mechanisms have been proposed. [20][21][22][23][24][25] Although there is some disagreement among the proposed mechanisms, it is widely accepted that the reaction mechanism includes the consecutive formation of organonitrogen species, isocyanates, cyanide, and ammonia through the reaction of nitrate species and hydrocarbonoxygenated species. 1,2 In addition, different nitrates or hydrocarbon-oxygenated species also exhibit different reactivity.…”