In situ magnetic resonance imaging study of the impregnation of γ-alumina pellets

Nowacka, Aleksandra; Moughames, J.; Adem, Ziad; Quoineaud, Anne-Agathe; Rolland, Matthieu; Guenneau, Flavien; Gédéon, A.

doi:10.1016/j.apcata.2015.07.014

Cited by 5 publications

(6 citation statements)

References 38 publications

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“…Typical impregnation times in the range of a few minutes to 1 or 2 h are employed for alumina in industry. , Residence times (corresponding to the experimental times or the time spent by the nickel solution inside the reactor) of between 10 and 940 min have been chosen to monitor the dynamics of the nickel and proton adsorption. Greater residence times have not been performed to avoid alumina dissolution. , The impregnation experiments are conducted at a temperature of 25 °C since alumina extrudates are typically impregnated under ambient conditions in industry.…”

Section: Methodsmentioning

confidence: 99%

“…On the other hand, many researchers studied the adsorption of cationic metal species, including nickel, from aqueous solutions on alumina structures. Among these researchers, some evaluated the distribution of the metallic species inside the solids at different aging times during impregnation experiments of alumina using magnetic resonance imaging or MRI, ,, Raman spectroscopy, , electron microprobe analysis, and most recently LIBS imaging. , They emphasized the effect of the metal concentration and the presence of additives in the impregnation solution on the metal distribution profiles inside the alumina solids. Others investigated the metal adsorption efficiency at equilibrium by monitoring the liquid phase in contact with alumina solids during batch experiments (mostly using inductively coupled plasma–optical emission spectroscopy or ICP–OES, atomic absorption spectroscopy or AAS, and UV/vis absorbance techniques). − ,,, These studies showed that the operating conditions (initial pH, initial metal concentration, adsorbent dosage, contact time, and temperature) impact the removal of metal species.…”

Section: Introductionmentioning

confidence: 99%

“…3,4 For decades now, it has been used as an inert support for metal-activated hydrotreatment catalysts prepared by the impregnation technique, such as Ni/γ-Al 2 O 3 catalysts applied in the dry reforming of methane, 5 Co/γ-Al 2 O 3 catalysts employed in Fischer−Tropsch processes, 3 and NiMo/γ-Al 2 O 3 or CoMo/γ-Al 2 O 3 catalyzing hydrodesulfurization reactions. 2,6 Such heterogeneous catalysts are commonly prepared in industry using the impregnation technique, even though other catalyst preparation techniques exist. 7 Two types of impregnation techniques have been identified: the dry (impregnation of dry solids) and wet (contacting solids with the solvent prior to impregnation) techniques.…”

Section: ■ Introductionmentioning

confidence: 99%

“…γ-Alumina or γ-Al 2 O 3 is a dehydrated phase of aluminum oxide obtained by the calcination of boehmite (or AlOOH) at approximately 500–700 °C . It is widely recognized for its low cost and advantageous mechanical and textural properties, such as thermal stability, acid/base properties, pore volume, pore size distribution, and high surface area compared to those of other aluminum oxide phases. , For decades now, it has been used as an inert support for metal-activated hydrotreatment catalysts prepared by the impregnation technique, such as Ni/γ-Al 2 O 3 catalysts applied in the dry reforming of methane, Co/γ-Al 2 O 3 catalysts employed in Fischer–Tropsch processes, and NiMo/γ-Al 2 O 3 or CoMo/γ-Al 2 O 3 catalyzing hydrodesulfurization reactions. , Such heterogeneous catalysts are commonly prepared in industry using the impregnation technique, even though other catalyst preparation techniques exist . Two types of impregnation techniques have been identified: the dry (impregnation of dry solids) and wet (contacting solids with the solvent prior to impregnation) techniques. , More recently, the use of γ-Al 2 O 3 as an adsorbent for the treatment of industrial wastewaters contaminated by heavy metals (e.g., nickel and cobalt) has been gaining more interest. − Both γ-alumina applications consist of contacting extrudates with aqueous solutions of the metal under certain operating conditions at which the metallic species in solution adsorb on the pore surface.…”

Section: Introductionmentioning

confidence: 99%

“…30 On the other hand, many researchers studied the adsorption of cationic metal species, including nickel, from aqueous solutions on alumina structures. Among these researchers, some evaluated the distribution of the metallic species inside the solids at different aging times during impregnation experiments of alumina using magnetic resonance imaging or MRI, 6,31,32 Raman spectroscopy, 32,33 electron microprobe analysis, 18 and most recently LIBS imaging. 25,34 They emphasized the effect of the metal concentration and the presence of additives in the impregnation solution on the metal distribution profiles inside the alumina solids.…”

Section: ■ Introductionmentioning

confidence: 99%

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Adsorption of Nickel Ions on the γ-Alumina Surface: Competitive Effect of Protons and Its Impact on Concentration Profiles

Fayad,

Couenne,

Sorbier

et al. 2023

Langmuir

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Mesoporous γ-alumina is used as an adsorbent in the decontamination of water from heavy metals (e.g., nickel and cobalt) and as a support for heterogeneous catalysts prepared by impregnation. In these cases, alumina extrudates are in contact with aqueous solutions containing precursors of the active metal phase to be deposited. The proton concentration (or pH) in the metal solution in contact with alumina can impact the adsorption efficiency of decontamination processes and the activities of catalysts. Yet, it is difficult to quantify the effect of the pH inside the pores since protons are not detected by classical imaging techniques. In this article, the effect of protons on nickel adsorption on alumina is evaluated using a novel technique coupling liquid analysis (pH, conductivity, and UV/vis) and laser-induced breakdown spectroscopy (or LIBS) analysis of concentration gradients inside the solid. Both methods are in excellent agreement. The results show a slow diffusion of protons inside alumina pores (diffusion continues even after 940 min), yielding high proton concentration gradients. On the other hand, the nickel species penetrate the extrudates faster but are slowly displaced by protons under certain operating conditions. As a result, different metal concentration profiles are obtained, depending on the initial pH and contact time. These findings are interesting in catalysis since they prove the possibility of controlling the deposition of the active metal on catalysts by regulating the operating conditions of impregnation. For typical industrial impregnation times (a few minutes to 1 to 2 h), protons do not have enough time to deeply penetrate inside extrudates, so the initial pH of the metal solution will have nearly no effect on the metal distribution. Conversely, decontamination processes have much longer contact times; therefore, lower initial pH values should have negative impacts on the adsorption efficiency due to the protons displacing the adsorbed nickel.

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