Hollow γ-Al2O3 microspheres as highly “active” supports for Au nanoparticle catalysts in CO oxidation

Abstract

Consisted of closely packed nanoflakes, γ-Al 2 O 3 hollow microspheres with ca. 4-6 μm in diameter, and 500-700 nm in shell thickness have been hydrothermally synthesized through utilizing Al(NO 3) 3 •9H 2 O as precursor, urea as precipitant agent and sulfate K 2 SO 4 , (NH 4) 2 SO 4 , or KAl(SO 4) 2 •12H 2 O as additive, followed by a calcination step. The samples were further characterized by thermogravimetric analysis, scanning electron microscope, x-ray powder diffraction, nitrogen adsorption, and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of adsorbed CO etc. The morphology of alumina products was strongly dependent on the presence of SO 4 2−. Then via a deposition-precipitation method, 3 wt.% Au nanoparticles supported on γ-Al 2 O 3 hollow microspheres exhibit excellent performance with a complete CO conversion at 0°C (T 100% =0°C) and 50 % conversion at −25°C (T 50% =−25°C). The good catalytic activity is associated with the special hollow microsphere structures assembled by nanoflakes of γ-Al 2 O 3 support. The DRIFTS confirms the presence of Au δ+ and Au 0 on the surface of γ-Al 2 O 3 hollow microspheres. As a contrast, Au catalyst prepared using alumina support with undefined morphology shows low activity under the same catalytic test conditions (T 100 % = 190°C, T 50 % =80°C). Keywords Hollow microspheres. γ-Al 2 O 3. Au catalyst. CO oxidation

Alumina hollow microspheres supported gold catalysts for low-temperature CO oxidation: effect of the pretreatment atmospheres on the catalytic activity and stability

“…The BET specific surface area and the pore volume of Al 2 O 3 were calculated as 209 m 2 /g and 0.66 cm 3 /g, respectively. These results are similar to our recent work [27]. The actual Au content is 0.53 wt% by ICP measurement.…”

“…Alumina hollow microspheres were prepared using a hydrothermal method [27]. In detail, 5 mmol of KAl(SO 4 ) 2 ·12H 2 O was dissolved in 50 mL of deionized water, and then 10 mmol of CO(NH 2 ) 2 dissolved in 50 mL of deionized water was added into the KAl(SO 4 ) 2 ·12H 2 O solution under vigorous stirring at room temperature for 0.5 h. The mixture was transferred into a Teflon-lined stainless steel autoclave and heated at 180°C for 3 h. After thorough washing and centrifugation, the solid was dried at 80°C and calcined at 600°C in a muffle oven for 2 h.…”

Deposition of aminosilane coatings on porous Al2O3 microspheres by means of dielectric barrier discharges

“…Porous ceramic particles based on metal oxides are facing continuously growing applications, particularly those composed of silica and alumina, due to their unique properties: high surface area, good mechanical, thermal and chemical stability, valuable catalytic activity, as well as the possibility of fabricating them in tunable micro and nano dimensions and pore sizes . In particular, their permeability to various gases and liquids makes ceramics with well‐developed open pores appealing and widely employable in many technological fields, as filters for molten metals, catalyst carriers, high temperature insulators, and lightweight structural materials . Furthermore, mesoporous nano ceramic particles are excellent candidates also for drug delivery and other biomedical applications …”

Experience in plasma production of hollow ceramic microspheres with required wall thickness

“…Such powders have gained widespread use, and they offer potential in many novel technological processes. Among such processes is the production of lightweight and buoyant materials [1], strong composite sound and heat insulators [2], heat-insulating paint coatings [3], lightweight proppants [4], radio transparent ceramics and electromagnetic interference isolation [5][6][7], explosives [8], catalysts [9], inertial fusion confinement targets [10,11], etc. Investigations into the possibility to extract helium out of natural gas [12] and to store hydrogen [13] using the selective gas permeability of ceramic hollow spheres are under way.…”