Lowering the Operating Temperature of Perovskite Catalysts for N₂O Decomposition through Control of Preparation Methods

Abstract

Discovering catalysts that can decompose N2O at low temperatures represents a major challenge in modern catalysis. The effect of preparative route on N2O-decomposition activity has been examined for a PrBaCoO3 perovskite catalyst. Initially, a citric acid preparation was utilised where the A site ratio was altered in order to increase phase purity. Comparable compositions were then prepared by an oxalic acid precipitation method and by a supercritical anti-solvent technique to produce perovskites with a higher surface area (> 30 m 2 g -1 ). By altering the A site ratio it was possible to reduce the temperature required to produce a pure phase perovskite whilst maintaining a higher-surface area.The use of the different preparation methods resulted in perovskites with varying properties, as determined by N2 adsorption, XPS, O2-TPD and H2-TPR. This work confirms the importance of lattice oxygen species that have high oxygen mobility for enhanced decomposition of N2O, as oxygen recombination is considered the rate-limiting step. Here, the formation of molecular oxygen is limited by surface adsorbed O species being within a distance at which oxygen recombination is possible. The most active PrBaCo-based catalyst did not have the highest percentage of lattice oxygen as shown by XPS, however, the catalytic activity could be correlated to the mobile oxygen species and high surface area. The PrBaCo-based catalyst prepared by supercritical anti-solvent converted 50 % of the N2O present in the feed (T50) at 410 °C, which represents a significant improvement over reported catalytic performance measured under similar conditions.

Hydrothermal microwave‐assisted synthesis of LaFeO3 catalyst for N2O decomposition

“…Lattice constants were determined by the equation for the orthorhombic unit cell:where h , k , l are Müller indexes, a , b , c —lattice constants, and d hkl —interplanar spacing which can be obtained from the Bragg's law:where n is an order of diffraction ( n = 1), λ —x‐ray wavelength, θ —angle of the diffraction. The average crystallite size ( D ) and microstrain (ε) were calculated by a Williamson‐Hall method, which can be expressed as a straight‐line equation, and these parameters can be obtained from the slope and intercept, respectively 36 :where β total is the total broadening of a peak, K —a shape factor.…”

“…All the noble metal based systems are supported catalysts, and the nature of the interactions of a noble metal with the support plays also a crucial role in their activity. [27][28][29] The main disadvantage of noble-metal catalysts is the high cost, so chemists are mostly looking for suitable catalytic materials from the second groupnon-noble-metal oxide catalytic systems 22 which include a wide range of oxide types such as bulk oxides, [30][31][32] spinels, 33,34 perovskites, hexaferrites, hydrotalcites [35][36][37][38][39][40][41] etc. The use of a support allows one to increase the specific activity of metal particles due to the enhanced dispersity, which is convincingly illustrated by examples of Fe 2 O 3 and Co 3 O 4 supported on ZrO 2 catalysts.…”

“…As a rule, in case of spinel-type oxides, alkali, transition metals, and lanthanides are used as promoters, [45][46][47][48][49][50][51][52][53][54][55][56][57][58] while for perovskite-like oxides and hexaaluminates, Ba, Sr, Bi, Sn are often suggested. [36][37][38][59][60][61] Also, in order to decrease the process temperature, the additional reducing agents in a gas mixture can be used, for example, carbon dioxide, methane, and ammonia. [62][63][64][65][66][67] It was shown that the preparation method also influences the catalytic activity.…”

“…Various chemical elements can be used as promoting agents. As a rule, in case of spinel‐type oxides, alkali, transition metals, and lanthanides are used as promoters, 45‐58 while for perovskite‐like oxides and hexaaluminates, Ba, Sr, Bi, Sn are often suggested 36‐38,59‐61 . Also, in order to decrease the process temperature, the additional reducing agents in a gas mixture can be used, for example, carbon dioxide, methane, and ammonia 62‐67 …”

“…Also, it was shown that in comparison with the precipitation method, combustion synthesis of LaNiO 3 results in a higher specific surface area and catalytic activity 73 . In a work by Richards et al, 36 advantages of a supercritical antisolvent technique were demonstrated for PrBaCo‐based perovskite catalysts. Thus, in order to achieve a high catalytic activity in the decomposition of nitrous oxide, each catalytic system requires an individual synthetic approach, and it is impossible to say in advance which method will be more efficient than other techniques for a particular catalytic system.…”