Effect of the Supported Pt on the Migration of Structural Ga Toward the Surface of Catalysts of the Pt/H[Ga]ZSM5 Type

Ethylene Hydrogenation over Pt/Ga2O3/Al2O3 Catalysts

“…For example, due to the addition of 1.3% Ga 2 O 3 (Pt1GaAl catalyst), the Pt dispersion increased (30% for the highest reduction temperature), contrasting with the decrease in the initial conversion (82% for the same reduction temperature). Similar results were presented by Melo et al [17], who found that the activity of the 1 wt.% Pt/H[Al]ZSM5 catalyst for toluene hydrogenation was 12 times higher than that of the 1 wt.% Pt/ H[Ga]ZSM5 catalyst, which had gallium incorporated in the zeolitic structure, whereas the Pt dispersion of the former was 1.6 times lower than that of the latter. This can be due to the Ga migration toward the surface of Pt particles, which should favor electronic and/or geometrical interactions between Pt particles and Ga species; resulting in the passivation of Pt metallic centers for the hydrogenation reactions [17].…”

“…Similar results were presented by Melo et al [17], who found that the activity of the 1 wt.% Pt/H[Al]ZSM5 catalyst for toluene hydrogenation was 12 times higher than that of the 1 wt.% Pt/ H[Ga]ZSM5 catalyst, which had gallium incorporated in the zeolitic structure, whereas the Pt dispersion of the former was 1.6 times lower than that of the latter. This can be due to the Ga migration toward the surface of Pt particles, which should favor electronic and/or geometrical interactions between Pt particles and Ga species; resulting in the passivation of Pt metallic centers for the hydrogenation reactions [17]. When the dose of Ga 2 O 3 was increased to 13% (Pt13GaAl catalyst), for any reduction temperature, the initial conversion decreased almost 100 times, while the dispersion diminished to the half.…”

“…These results also imply that the coverage of Pt particles by reduced Ga species, such as Ga 2 O and GaO + [16][17][18][19][20]22], hindered the ethylene hydrogenation. The higher the reduction temperature, the higher the amounts of these species that can be formed and, therefore, the higher the influence on catalytic activity can be observed.…”

“…However, the decreases in such ratios were also significant for the lower reduction temperature (350°C), about 49% and 87% in the H/Pt ratio and 55% and 92% in the CO/Pt ratio for the Pt13GaAl and PtGa catalysts, respectively, compared to the values of these ratios in the PtAl catalyst. Therefore, this decrease in dispersion associated to the addition of gallia can attribute to an intimate contact between Pt particles and partially reduced gallium species formed during the reduction treatment, where these species could encapsulate or block Pt particles [10,[16][17][18].…”

Delivering a Modifying Element to Metal Nanoparticles via Support: Pt–Ga Alloying during the Reduction of Pt/Mg(Al,Ga)Ox Catalysts and Its Effects on Propane Dehydrogenation

“…These results are in agreement with the literature that has suggested that Pt nanoparticles play a crucial role in the reduction of a modifying element from the HT framework. 35,36,63 Most probably, Pt nanoparticles dissociate molecular hydrogen and make it available for reduction of a modifying element from the support. 64 A freshly prepared catalyst without Ga, i.e., Pt/HT-0Ga, was also subjected to a reduction treatment to exclude possible changes not related to Pt−Ga alloying.…”