Silica deposition as an approach for improving the hydrothermal stability of an alumina support during glycerol aqueous phase reforming

Abstract

A B S T R A C TSilica deposition on the benchmark aqueous phase reforming (APR) catalyst Pt/γ-Al 2 O 3 is studied to prevent or limit hydrolytic attack of the support under hydrothermal APR conditions, for which boehmite formation by support hydration is a known cause for catalyst deactivation. Tetraethyl orthosilicate (TEOS) is employed as a silicon source in a straightforward liquid-phase, silylation process followed by catalyst calcination and reduction. Characterization by X-ray diffraction, temperature-programmed desorption of NH 3 , infrared, 27 Al nuclear magnetic resonance and X-ray photoelectron spectroscopy of the fresh catalysts suggests that silica addition occurs preferentially on the support surface, resulting in weak Brønsted acid sites as well as in the formation of Si-O-Al linkages at the expense of specific surface Lewis acid sites. Silylation and calcination of Pt/γ-Al 2 O 3 causes partial blockage of the metal surface area (12% loss), whereas γ-Al 2 O 3 surface silica modification prior to Pt deposition makes controlled metal deposition difficult. Catalytic performance tests show the overcoated samples to be active in the APR of 5 wt% glycerol, albeit with lower H 2 production rates compared to the benchmark catalyst. Characterization of spent APR catalysts clearly demonstrates that silylation/calcination treatments effectively slows down the transformation of the γ-Al 2 O 3 support due to the formation of a Si-O-Al interface. Overall, the lifetime of the catalyst is increased three-fold as a result of the surface overcoating treatment, with repetitive recycling ultimately leading to loss of the protective silica layer.

Reactivity of shape-controlled crystals and metadynamics simulations locate the weak spots of alumina in water

“…Albeit not fully described at the atomic scale yet, the decomposition of γ-Al 2 O 3 was shown to proceed, at the macroscopic scale, through a sequential mechanism involving first dissolution of Al atoms, and then precipitation thereof into the undesired hydroxides 16,24 . These structural changes can be retarded by tuning the surface chemical composition: silica deposition 26 , presence of metallic nanoparticles 12 , or impregnation with metal ions 27 . They are also impacted by the content of the solution: pH 24 but also presence of polyols 28 or polyphenols 25 .…”

Increasing the activity of the Cu/CuAl2O4/Al2O3 catalyst for the RWGS through preserving the Cu2+ ions

“…Layer deposition techniques could be improved by several strategies to inhibit or suppress site blockage, which can minimize this negative effect. 17,18 In this study, we added a silica layer through a controlled surface sol-gel method to protect Cu nanoparticles impregnated on Al 2 O 3 during the high temperature calcination step that forms the desired copper aluminate phase (catalyst labelled as CuAlSi-900). The schematic is shown in Fig.…”

A comprehensive study of indole catalytic hydrodenitrogenation under hydrothermal conditions

“…However, the size increased considerably after indole hydrothermal HDN reaction at 400°C for 60 min, as displayed in Figure 13B. Such an observation may be caused by the collapse of the pore structure of the support γ‐Al 2 O 3 in the presence of high‐temperature water vapor, 36 so the separated metal particles aggregated together with the decrease of the specific surface area of γ‐Al 2 O 3 during the HTL process. Scanning electron microscope (SEM) image and elemental distribution of Ni of the used catalyst, shown in Figure 13D,E, respectively, demonstrate that the Ni catalyst would be more easily clustered than the Ru noble metal, which is in line with our previous research that the monometallic Ni catalyst has a significantly broader particle size distribution than the Ni 85 M 15 (M = Cu, Pd, Pt, and Ru) bimetallic compounds 20a .…”