Catalytic Activity and Selectivities of Metal Oxides and Pt/Al₂O₃ for NH₃ Combustion

Abstract

Catalytic activity and selectivities of metal oxides and Pt/Al 2 O 3 were evaluated for the combustion of NH 3 , which is considered a carbon-free energy source. Catalytic NH 3 combustion using 3d transition metal oxides for the stoichiometric NH 3 O 2 reaction showed the following order of activity: MnO 2 > Co 3 O 4 > CuO > Fe 2 O 3 μ V 2 O 5 > NiO. This order implies that the activity increases with decreasing oxygen bond energy of the metal oxides. CuO exhibited higher N 2 selectivity than the other transition metal oxides.The investigation of more efficient and cleaner alternative fuel sources is imperative because of the excessive consumption of finite fossil fuel resources and the risks associated with the use of nuclear power. Recently, NH 3 has been considered a renewable and carbon-free energy source due to its high energy density (3160 W h L ¹1) and negligible thermal NO x emission. 13 However, in comparison with fossil fuels, NH 3 as a fuel poses the following problems: (1) high ignition temperature, (2) low combustion rate, and (3) N 2 O and fuel NO x production. Therefore, the development of new NH 3 combustion systems is necessary. One possible candidate is catalytic combustion, which is a promising technique for decreasing emissions from hydrocarbon-based (CH 4 , C 3 H 6 , etc.) fuels and has been actively studied for use in gas turbines, boilers, and jet engines in the 1980s. 4,5 Catalytic combustion has many advantages over conventional non-catalytic combustion, as NO x emission is greatly diminished by the low operating temperatures, and high efficiency can be attained through stable combustion. By applying a novel catalytic combustion system to NH 3 fuel, it is expected that low-temperature ignition as well as negligible emission of NO x can be achieved. To the best of our knowledge, there are no published studies regarding the catalytic combustion of NH 3 . In this study, to understand the basis of the catalytic NH 3 combustion properties of metal oxides and Pt/Al 2 O 3 , their combustion activity and product selectivities were evaluated. In addition, our study was extended to demonstrate the relationship between the NH 3 combustion activity of metal oxides and the oxygen bond energy.Commercially available metal oxides (Table S1, Supporting Information (SI)) were used for the catalytic NH 3 combustion. As a reference, 1.0 wt % Pt/γ-Al 2 O 3 was prepared by a conventional wet-impregnation method using an aqueous solution of [Pt(NH 3 ) 2 (NO 2 ) 2 ] (Tanaka Kikinzoku Kogyo), and subsequent calcination in air at 600°C for 3 h. Metal oxides and as-prepared Pt/Al 2 O 3 were characterized by X-ray diffraction (XRD), X-ray fluorescence, gas adsorption (BrunauerEmmettTeller (BET) surface area, and NH 3 -temperature-programmed desorption (TPD)). Catalytic NH 3 combustion was conducted in a flow reactor at atmospheric pressure (10°C min ¹1 , 1.0% NH 3 , 018% O 2 , He balance, 100 cm 3 min ¹1 and W/F = 5.0 © 10 ¹4 g min cm ¹3 ). The dependence of NH 3 combustion activity and product selectivities on the...

Bottom‐Up Design of a Copper–Ruthenium Nanoparticulate Catalyst for Low‐Temperature Ammonia Oxidation

“…[10][11][12][13] Fewstudies have been devoted to stoichiometric mixtures. [3,14,15] Thus,there is aneed to develop new ammonia combustion systems.…”

“…[15] The combustion reaction is also easier to sustain for catalytic reaction. [15] The combustion reaction is also easier to sustain for catalytic reaction.…”

“…One possible way to avoid the aforementioned issues is by stoichiometric catalytic combustion, which has many advantages over conventional non-catalytic combustion as the ignition temperature is decreased and NOx emission is reduced because of the low operating temperature. [15] The combustion reaction is also easier to sustain for catalytic reaction. Herein, we present abottom-up approach to design anovel core-shell nanoparticulate catalyst of ruthenium (Ru) and copper (Cu).…”

<i>Operando</i> XAFS studies of supported copper oxides for catalytic ammonia combustion

“…Previously, we proposed novel catalytic NH 3 combustion systems that enable low ignition temperatures as well as negligible N 2 O/NO x emissions, 14)16) and reported that the NH 3 combustion activity of metal oxides increases with a decrease in their metaloxygen bond energy. 14) In addition, a novel catalyst, copper oxide (CuO x ) supported on aluminum oxide borates (10Al 2 O 3 ·2B 2 O 3 : 10A2B) with high performance for NH 3 combustion, was successfully prepared. 15) Although CuO x -based catalysts have also been widely studied for the selective oxidation of NH 3 emissions to reduce air pollution, 17), 18) there are no published studies of the catalytic local structures during NH 3 combustion and/or the oxidation reaction over the well-known supported CuO x .…”

Bottom‐Up Design of a Copper–Ruthenium Nanoparticulate Catalyst for Low‐Temperature Ammonia Oxidation

“…The main body of research into ammonia oxidation is devoted to the ammonia slip reaction from diesel engines where the reaction is operated in an excess of oxygen . Few studies have been devoted to stoichiometric mixtures . Thus, there is a need to develop new ammonia combustion systems.…”