Effect of the Nickel Precursor on the Impregnation and Drying of γ-Al₂O₃ Catalyst Bodies:  A UV−vis and IR Microspectroscopic Study

Abstract

The elemental preparation steps of impregnation and drying of Ni/γ-Al 2 O 3 catalyst bodies have been studied by combining UV-vis and IR microspectroscopy. The influence of the number of chelating ligands in [Ni(en) 2+ precursor complexes (with en ) ethylenediamine and x ) 0-3) has been investigated. UV-vis measurements after impregnation showed that, regardless of the en:Ni 2+ ratio in the precursor solution, Ni 2+ was already detected in the core of the pellets 5 min after impregnation. The alumina support did bring about, however, gradients in the nature of the Ni 2+ species upon first contact with the lowest en:Ni 2+ ratio solutions, but these gradients disappeared after 30-60 min of impregnation. After 60 min, UV-vis seemed to indicate Ni-O-Al interactions between Ni 2+ and the support, when water was initially part of the first coordination sphere of Ni 2+ , which was supported with the results obtained after drying. For dried samples, UV-vis showed a gradient of [Ni(en) x (H 2 O) 6-2x ] 2+ inside the pellets, with an en-poor region in the core and an en-rich region in the edges of the catalyst bodies, when [Ni(en) were the starting complexes. IR microspectroscopy confirmed these en radial profiles, while EDX measurements showed that an Ni 2+ egg-shell distribution goes hand-in-hand with an egg-shell distribution of en. The number of en ligands determined the interactions of Ni 2+ with the support after impregnation and controlled the redistribution of metal-ion species during drying. Moreover, when redistribution of Ni 2+ occurred during drying, its transport toward the outer rim of the extrudates came about together with changes of the local en:Ni 2+ ratio.

CO2 Hydrogenation Over Ni-Based Zeolites: Effect of Catalysts Preparation and Pre-reduction Conditions on Methanation Performance

“…Figure 1 shows the UV-Vis spectra obtained for the Ni catalysts dried using conventional heating and microwave irradiation after impregnation. According to the literature [8,[26][27][28], bands around 300, 390, 429 and 725 nm are ). It can be observed that, when using conventional heating (5 %NiUSY 500 , reference catalyst [8]), NiO is the main Ni specie observed (clearly seen by the presence of the band at 300 nm) while, when using microwaves, octahedral Ni 2?…”

Interfacial Impregnation Chemistry in the Synthesis of Nickel Catalysts Supported on Titania

“…[38,42,43] It is well known that the bands due to the spin-allowed transitions move towards the infrared as Dq decreases. [44,45] The value of 10Dq for the deposited species (as calculated from the energy of the 3 …”

Space-Resolved Profiling Relevant in Heterogeneous Catalysis

“…The preparation, i.e. impregnation and drying processes of Ni/ c-Al 2 O 3 catalyst bodies were investigated by IRM combined with UV-Vis spectroscopy, giving insight into the influence of chelating ligands of precursor complexes on the distribution of the active metal sites over the bodies [23]. Recently, the first in situ, space-and time-resolved IRM study of styrene oligomerization within the H-ZSM-5 micropores was demonstrated using a highly brilliant synchrotron IR beam and the non-uniform product distribution within the crystal was rationalized [24].…”

“…The combined studies revealed time-dependent gradients of precursor concentration profiles in a catalyst body during catalyst preparations of CoMo/c-Al 2 O 3 hydrodesulphurization catalyst [48,49,140], providing detailed insight into the impregnation and drying processes. UV-Vis-NIR was also combined with IR microscopy to investigate the effect of Ni precursor on the distribution of catalytic active sites during impregnation and drying processes of Ni/c-Al 2 O 3 catalyst preparation [23]. At a reactor scale, multiple UV-Vis probes were used to monitor chemical processes at different positions of a chromium oxide catalyst bed during propane dehydrogenation [141].…”