Abstract:A series of unconventional nano-sized Zn-doped ZnZrO-x catalysts are applied for the first time to the direct dehydrogenation of isobutane to isobutene.
“…Considering the EPR results (Figure ) and according to Silva‐Calpa et al., McFarland & Metiu and Liu et al., it can be suggested that Zn +2 substitutes Zr +4 in the t ‐ZrO 2 lattice generating oxygen vacancies and coordinatively unsaturated Zr 4+ ions (cus). The oxygen vacancies can be associated with strong basic sites whereas the cus species with Lewis acid sites.…”
Section: Resultsmentioning
confidence: 75%
“…Indeed, replacing Zr +4 with Zn +2 makes the ZrO 2 surface more electrophilic. As oxygen is also electrophilic, it is easily displaced from the oxide surface generating vacancies . Silva‐Calpa et al .…”
Section: Resultsmentioning
confidence: 99%
“…Recently, Liu et al . have showed that the ZnZrO 2 catalyst exhibits high activity for the alkanes dehydrogenation, which was associated with oxygen vacancies and cus pairs generated by the presence of Zn +2 in the ZrO 2 lattice.…”
The t‐ZrO2 doped with Zn catalyst and t‐ZrO2 as reference were employed in the butadiene synthesis from ethanol. Both catalysts were characterized by NH3‐TPD, CO2‐TPD, TPSR, the MPV model reaction, ICP, BET and EPR. Adding 0.2 wt% Zn to t‐ZrO2, the selectivity to butadiene increases three fold whereas the one to ethylene decreases. When ZrO2 is doped, the number of basic sites increases and the number of acid sites decreases. The TPSR spectra indicate that the acetaldehyde generation is the rate limiting step of the butadiene synthesis. The slowest step of the acetaldehyde generation is the H abstraction by a strong basic site. The EPR spectra show the replacement of Zr4+ by Zn2+ in the lattice of the t‐ZrO2 oxide. This phenomenon forms pairs of oxygen vacancies and coordinatively unsaturated Zr4+ ions (cus), which are strong basic sites and acid sites, respectively. Doping ZrO2 with Zn, the ethanol dehydrogenation and the butadiene synthesis are promoted not only due to the changes in the acidity and basicity of the catalyst but mainly because of the generation of oxygen vacancies and cus pairs during the reaction. These oxygen vacancies seem to behave as strong Brønsted basic sites.
“…Considering the EPR results (Figure ) and according to Silva‐Calpa et al., McFarland & Metiu and Liu et al., it can be suggested that Zn +2 substitutes Zr +4 in the t ‐ZrO 2 lattice generating oxygen vacancies and coordinatively unsaturated Zr 4+ ions (cus). The oxygen vacancies can be associated with strong basic sites whereas the cus species with Lewis acid sites.…”
Section: Resultsmentioning
confidence: 75%
“…Indeed, replacing Zr +4 with Zn +2 makes the ZrO 2 surface more electrophilic. As oxygen is also electrophilic, it is easily displaced from the oxide surface generating vacancies . Silva‐Calpa et al .…”
Section: Resultsmentioning
confidence: 99%
“…Recently, Liu et al . have showed that the ZnZrO 2 catalyst exhibits high activity for the alkanes dehydrogenation, which was associated with oxygen vacancies and cus pairs generated by the presence of Zn +2 in the ZrO 2 lattice.…”
The t‐ZrO2 doped with Zn catalyst and t‐ZrO2 as reference were employed in the butadiene synthesis from ethanol. Both catalysts were characterized by NH3‐TPD, CO2‐TPD, TPSR, the MPV model reaction, ICP, BET and EPR. Adding 0.2 wt% Zn to t‐ZrO2, the selectivity to butadiene increases three fold whereas the one to ethylene decreases. When ZrO2 is doped, the number of basic sites increases and the number of acid sites decreases. The TPSR spectra indicate that the acetaldehyde generation is the rate limiting step of the butadiene synthesis. The slowest step of the acetaldehyde generation is the H abstraction by a strong basic site. The EPR spectra show the replacement of Zr4+ by Zn2+ in the lattice of the t‐ZrO2 oxide. This phenomenon forms pairs of oxygen vacancies and coordinatively unsaturated Zr4+ ions (cus), which are strong basic sites and acid sites, respectively. Doping ZrO2 with Zn, the ethanol dehydrogenation and the butadiene synthesis are promoted not only due to the changes in the acidity and basicity of the catalyst but mainly because of the generation of oxygen vacancies and cus pairs during the reaction. These oxygen vacancies seem to behave as strong Brønsted basic sites.
“…Alternatively, the O vacancies are associated with CO dissociation or formate decomposition to methoxy species, both suggested as the rate-limiting step of the methanation reaction. The CO 2 methanation mechanisms employing vacancy–cus pairs 12 are described in detail in the Results and discussion section.…”
The Ni/ZrO2, Ni/Mg(Al)O, and Ni/SiO2 catalysts were employed in the CO2 methanation. The catalysts were characterized by XPS, XRF, XRD (Rietveld refinement method), TPR, EPR, BET, CO2+H2-TPSR, CO+H2-TPSR, CO2-TPD, CO-TPD,...
“…The support materials, Al 2 O 3 [11], SiO 2 [6], ZrO 2 [12,13] and zeolite [3,14], can also affect catalytic performance on account of the significant differences in textural properties. Especially, the Mg(Al)O (c) by-product selectivity (reduction conditions: T = 600 °C, t = 2.5 h; reaction conditions: T = 600 °C, weight hourly space velocity (WSHV) = 3 h −1 , atmospheric pressure in the gas mixture of C3H8:H2:N2 molar ratio = 8:7:35; reaction time: 30 h for H2/N2 and 14 vol % H2/N2 reduced catalyst, 26 h for C3H8/H2/N2-reduced catalyst, 17 h for C3H8 and CO-reduced catalyst).…”
The effect of reduction atmospheres, H2/N2, C3H8/H2/N2, C3H8 and CO, on the structure and propane direct dehydrogenation performance of PtIn/Mg(Al)O/ZnO catalyst derived from ZnO-supported PtIn-hydrotalcite was studied. The physicochemical properties of the as-prepared and used catalytic system were characterized by various characterization methods. The results show that the dehydrogenation performance, especially the stability of the PtIn/Mg(Al)O/ZnO catalyst, was significantly improved along with the change in reduction atmosphere. The highest catalytic activity (51% of propane conversion and 97% propylene selectivity), resistance toward coke deposition, and stability for more than 30 h were achieved with the H2/N2-reduced catalyst. The optimal dehydrogenation performance and coke resistance are mainly related to the high Pt dispersion and In0/In3+ molar ratio, strong Pt–In interaction and small metal particle size, depending on the nature of the reduction atmospheres. The reconstruction of meixnerite favors the stability and coke resistance to some extent.
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