Selective Oxidation of Methanol to Hydrogen over Gold Catalysts Promoted by Alkaline‐Earth‐Metal and Lanthanum Oxides

Abstract

A series of alumina-supported gold catalysts was investigated for the CO-free production of hydrogen by partial oxidation of methanol. The addition of alkaline-earth metal oxide promoters resulted in a significant improvement of the catalytic performance. The methanol conversion was ca. 85 % with all studied catalyst materials, however, the selectivity for hydrogen increased from 15 % to 51 % when going from the unpromoted to a BaO-promoted catalyst. The formation of the undesired byproducts CO, methane, and dimethyl ether was considerably reduced as well. The observed trend in catalyst performance follows the trend in increasing basicity of the studied promoter elements, indicating a chemical effect of the promoter material. Superior catalytic performance, in terms of H(2) and CO selectivity, was obtained with a Au/La(2)O(3) catalyst. At 300 degrees C the hydrogen selectivity reached 80 % with only 2 % CO formation, and the catalyst displayed a stable performance over at least 24 h on-stream. Furthermore, the formation of CO was found to be independent of the oxygen concentration in the feed. The commercial lanthanum oxide used in this study had a low specific surface area, which led to the formation of relative large gold particles. Therefore, the catalytic activity could be enhanced by decreasing the gold particle size through deposition on lanthanum oxide supported on high-surface-area alumina.

Development of novel supported gold catalysts: A materials perspective

“…Gold catalysts based on oxidemodified Al 2 O 3 supports include Au/MgO/Al 2 O 3 [189][190][191], Au/MnO x /Al 2 O 3 [192][193][194], Au/FeO x /Al 2 O 3 [192][193][194][195][196], Au/CoO x /Al 2 O 3 [192,194], Au/ZnO/Al 2 O 3 [192,197] [199], and Au/CeO 2 /Al 2 O 3 [200][201][202][203]. In particular, Nieuwenhuys and coworkers tested the performance of Al 2 O 3 -based gold catalysts in a number of reactions, and established that MgO/Al 2 O 3 [189], BaO/Al 2 O 3 [204,205], ZnO/Al 2 O 3 [197], and ZrO x /Al 2 O 3 [197] could all stabilize gold nanoparticles against thermal sintering.…”

An Attempt to Selectively Oxidize Methane over Supported Gold Catalysts

“…An onset for methane combustion of around 150°C was found for their most active Au/CoO x catalyst. In the light of these results, it must be noted that methanol oxidizes over gold catalysts already at *80°C [31]. Therefore, if small amounts of methanol would be formed, its survival under the conditions needed for methane activation is questionable.…”

“…Gold catalysts have shown remarkable activities and selectivities in selective oxidation of CO [23][24][25][26], alcohols [27][28][29][30][31][32], and olefins [33][34][35] already. These topics are covered by extensive reviews, published in the last decade [36][37][38][39][40][41][42][43][44][45].…”

Synthesis and characterization of a binary system La2O3–SiO2 prepared by combustion method

“…Lanthanum oxide has a lot of attractive properties that permitted its wide applications, e.g., as catalysts [1,2], support for metal [3,4], dielectric material [5,6] and optical filters [7]. In our previous work [8,9], we have studied the amorphous nature of SiO 2 -La 2 O 3 system even for the largest quantity of lanthanum oxide (1:1 Si/La), which prefers crystalline forms.…”

“…The La 2 O 3 /SiO 2 system was prepared on the basis of a modified procedure described in details in the previous paper [9]. The binary oxide gel system was obtained by mixing the appropriate amounts of TEOS and a solution of La(CH 3 COO) 3 in anhydrous acetate acid. The homogenous solutions were closed in a reactor upon stirring and heated at 353 K for 48 h. The gels were dried at 393 K by slow evaporation for 72 h. Synthesised binary oxide gels were ignited on the evaporating dish, initiating a self-propagating combustion process, and dark grey loose product was obtained after the combustion was completed (Fig.…”