Abstract
This study describes the phenomena involved during the regeneration of an aged industrial hydrodesulfurization catalyst (CoMoP/Al2O3) using a non-thermal plasma at a low temperature (200 °C). The changes occurring during regeneration were studied by characterizing spent, partially, and fully regenerated catalysts by XRD, Raman, TEM spectroscopy, and the coke deposited on the catalyst surface by Laser desorption/ionization time-of-flight mass spectrometry (LDI TOF/MS). The coke is a mixture of several polycyclic molecules, the heaviest with a coronene backbone, containing up to seven sulfur atoms. This kinetic study shows that the oxidation rate depends on the nature of the coke. Hence, explaining the formation of VOCs from heavy polycyclic carbon molecules without complete oxidation to CO2. However, XRD and Raman spectroscopies evidence CoMoO4 formation after a long treatment time, indicating hot spots during the regeneration.
Highlights
Non-thermal plasma (NTP) attracts a lot of interest because this technology is capable of carrying out thermodynamically unfavorable reactions, for example, hydrocarbons reforming [1], CO2 hydrogenation, ammonia synthesis [2], and VOCs elimination [3,4]
We have found that the regeneration of an aged HDS catalyst by non-thermal plasma is much more complicated than a coked zeolite [17]
MoS2 slabs rapidly oxidize in molybdenum oxide, and after an extended period, due to a local increase of the temperature inside the dielectric barrier discharge (DBD) reactor, appears on the alumina surface, other oxides like Co3 O4, CoMo6, or AlMO6 and CoMoO4, species known to be refractory to sulfidation
Summary
Non-thermal plasma (NTP) attracts a lot of interest because this technology is capable of carrying out thermodynamically unfavorable reactions, for example, hydrocarbons reforming [1], CO2 hydrogenation, ammonia synthesis [2], and VOCs elimination [3,4].The combination with plasma and catalysis has been largely described to perform many reactions [5,6]; some studies were reporting using plasma to prepare [7] and regenerate catalysts [8,9]. Non-thermal plasma (NTP) attracts a lot of interest because this technology is capable of carrying out thermodynamically unfavorable reactions, for example, hydrocarbons reforming [1], CO2 hydrogenation, ammonia synthesis [2], and VOCs elimination [3,4]. As indicated in the paper: “The 2020 plasma catalysis roadmap” [5], non-thermal plasma treatment appears as an effective technique for removing coke from various spent catalysts. The main advantage of oxygen plasma is that it creates O-atoms through simple dissociation of O2 by electron collisions, the active species being: O2 + , O− , O2 − and. Using a noble gas such as argon or helium with oxygen is effective for catalyst decoking, as shown by Khan and Al Jalal [11]. The authors showed that atomization of O2 was improved with He and Ar compared to N2 , most probably due to reactions between O atoms and N forming species such as NO, NO2 , N2 O, and N2 O5
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