Progress in the synthesis and applications of hexaaluminate-based catalysts

Abstract

The development of materials that can exhibit thermal resistance at very high temperatures, thus allowing them to be applied as catalysts and thermal insulators, amongst other possible uses, is a research subject of great interest. This is the case for hexaaluminates, a class of hexagonal aluminate compounds with a unique structure that are stable at very high temperatures up to 1600 o C and exhibit exceptional resistance to sintering and thermal shock, thus making them attractive catalysts for high-temperature applications. In this review, the structure of hexaaluminates is presented first. The most recent advances in synthetic methods (sol-gel, reverse microemulsion, hydrothermal synthesis, carbontemplating, solution combustion synthesis and freeze drying methods) are discussed subsequently, with the aim of maximizing textural properties and including in their structure metals known to be active in catalytic applications, such as combustion of CH4, partial oxidation and dry reforming of CH4 to produce synthetic gas, and the decomposition of N2O.Finally, other applications, such as their function as a thermal barrier, are also addressed.

Anisotropic Rh3+ Diffusion in Layered Hexaaluminate Mitigates Thermal Deactivation of Supported Rhodium Catalysts

“…Since the 1980s, hexaaluminate compounds, such as LaMgAl 11 O 19 , including β-alumina and magnetoplumbite-type layered structures, have been investigated as thermally stable catalyst supports in various fields of application. − Even after calcination at 1200 °C, the material maintains a larger surface area of ≥20 m 2 g –1 , whereas γ-Al 2 O 3 sinters into large agglomerates of α-Al 2 O 3 with a low surface area of <5 m 2 g –1 . To reduce the negative interactions with Rh 2 O 3 and improve the thermostability of Rh catalysts in a high-temperature oxidizing environment, we recently reported another advancement in hexaaluminate support materials .…”

Promoting Dry Reforming of Methane Catalysed by Atomically‐Dispersed Ni over Ceria‐Upgraded Boron Nitride

“…Great efforts including addition of catalysts promoters, [9,10] alloying with second metals, [11] and fabrication of confined structures [12][13][14] were devoted to develop high-performance Nibased catalysts for DRM. The inhibition of metal sintering by immobilizing Ni nanoparticles via confining strategy was particularly efficient to overcome carbon deposition.…”

Catalyst Deactivation via Rhodium–Support Interactions under High-Temperature Oxidizing Conditions: A Comparative Study on Hexaaluminates versus Al2O3

“…A possible candidate for replacing Al 2 O 3 as a support for Rh catalysts is an Al-based composite oxide. Among the binary and ternary oxide systems, we are mainly interested in the hexaaluminate compounds, which are known to be thermostable support materials with large specific surface areas. − In fact, the specific surface area of over 20 m 2 g –1 is retained even upon heating at 1200 °C, compared with less than 5 m 2 g –1 when transition Al 2 O 3 sinters into nonporous agglomerates of α-Al 2 O 3 . , The retention of the large surface area is closely related to the crystal structure, which is known to be the β-alumina or the magnetoplumbite type of the hexagonal layered structure family. , Although various researchers have studied hexaaluminates as a support for Rh, − no studies have been conducted in relation to the reactivity at the metal–support interface.…”