Silicalite-1 zeolite acidification by zinc modification and its catalytic properties for isobutane conversion

Abstract

A series of Zn-modified Silicalite-1 (S-1) zeolites (Zn x /S-1) were prepared by the wetness-impregnation method and applied in the catalytic conversion of isobutane. The structure and location of Zn species in Zn x /S-1 were investigated using UV-Vis and N 2 physical adsorption. The acidity and origin of the acid sites in Zn x /S-1 were studied by NH 3 -temperature programmed desorption and Fourier-transform infrared analysis. The catalytic performance of Zn x /S-1 for isobutane conversion was investigated in a fixed-bed microreactor. In the experiments, the acidity of S-1 zeolite was dramatically increased by modification with Zn, with both Lewis and Brønsted sites identified in Zn x /S-1. The relationship between Brønsted acid sites and Zn-OH groups on ZnO clusters of Zn x /S-1 was also revealed for the first time.Furthermore, Zn x /S-1 catalysts exhibited excellent catalytic performances in both isobutane dehydrogenation and butene isomerization reactions. A high selectivity of total butene products ranging from 84.6 to 97.2 was achieved on the catalysts with different Zn loadings. Moreover, the linear correlation between isobutane conversion and the acid amount (determined by NH 3 -TPD) confirmed that the weak-to-medium acid sites in Zn x /S-1 should play a key role in isobutane conversion.

Isobutane Dehydrogenation Assisted by CO2 over Silicalite‐1‐Supported ZnO Catalysts: Influence of Support Crystallite Size

“…The TG and IR results reveal that the total amount of silanols as well as silanol distribution on these Silicalite‐1 supports are different from each other, albeit they have the same topology and similar texture properties. As seen from Figure B, after supporting ZnO on Silicalite‐1 (5% Zn), there is an obvious decrease in the intensity of three bands, especially the band at 3490 cm –1 , which is due to the interaction of Zn species with the support–OH groups . This is indicative of a decrease in the number of silanol groups via consuming the exposed hydroxyl groups.…”

“…Three types of –OH groups can be found. The intense and sharp peak at 3739 cm –1 is assigned to isolated silanol groups located on the external surface, and the small peak at 3686 cm –1 is ascribed to vicinal silanol groups located inside the micropores . The strong broad peak at around 3490 cm –1 is generally attributed to nest silanol groups that comprise a number of silanol groups interacting through extended hydrogen bonding .…”

Facile synthesis of ordered mesoporous zinc alumina catalysts and their dehydrogenation behavior

“…33,34 The detailed calculation result was in Table 2. As displayed, all the 9832 | RSC Adv., 2019, 15,35 Note that the total and weak acidic sites gradually increased, while the strong acidic sites decreased slowly with the increase of Zn content until 10%. When the Zn content reached 15%, the total acidic strength of this catalyst declined sharply, which may due to bulk ZnO has rarely acidic sites (Fig.…”

“…It was well established that weak and medium acid sites played a key role to isobutane conversion in dehydrogenation reaction. 15 Isobutane dehydrogenation is an endothermic reaction in thermodynamics, which need relatively high temperature to obtain excellent isobutene yield. The effect of reaction temperature on catalytic activity of 10%Zn/Al 2 O 3 catalyst was investigated in Fig.…”

“…Liu et al reported that 27.5% isobutane conversion and 83.8% isobutene selectivity obtained in isobutane dehydrogenation over Zn/S-1 catalyst, because strong acid sites were absent. 15 Moreover, Zn/Ti thin lm and Zn/Ga oxide catalyst has also been referred in isobutane dehydrogenation. 16,17 Recently, ordered and adjustable mesoporous alumina materials have drawn research much attention.…”