Effect of the Cr2O3 Promoter on Pt/WO3-ZrO2 Catalysts for n-Heptane Isomerization

Abstract

Isomerate, the product of a light naphtha Isomerization unit, is a clean, high-octane gasoline blending component, which is free of sulfur content, aromatics, and olefins. However, the isomerization of the long-chain alkanes, such as n-heptane, is pretty difficult. As a result, this process has not been commercialized yet. In recent years, much attention has been paid to Pt/WO 3 /ZrO 2 as an n-heptane isomerization catalyst due to its good thermal stability, strong acidity, simplicity of preparation, reusability and good isomerization activity. In this work, the Pt/WO 3 /ZrO 2 catalyst was modified by various loading of metal Cr to improve the catalytic performance. The effects of WO 3 content, Cr metal loading and calcination temperature on the catalyst characters and catalytic activity were studied. It is shown that Cr-Pt/WO 3 /ZrO 2 with the loading of 18 wt% WO 3 and 1.0-1.4 wt% Cr, prepared at the calcination temperature of 800 • C, has the highest activity. It was found that the octane number increases by 28 units through the isomerization of light naphtha feedstocks. In addition, the study on the stability of Cr-Pt/WO 3 /ZrO 2 indicates that the catalyst is not deactivated after 500 h of the n-heptane isomerization reaction.Arata and Hino [6] because of its good stability both in reducing and oxidizing conditions [7]. While the WO 3 /ZrO 2 type catalyst shows high selectivity in the isomerization reaction of linear alkane, the catalyst activity is relatively low and the degree of cracking is too high [8]. Thus, the catalyst needs to be modified to meet the industrial production requirements. The catalyst consisting of Pt deposited on WO 3 /ZrO 2 for n-heptane isomerization has attracted the attention of a large number of researchers as the most promising catalyst [9,10]. The structure of the WO 3 /ZrO 2 catalyst varies depending on the WO 3 content [11,12], leading to different catalyst activities. The structure and properties of this kind of catalyst can be modified by changing the WO 3 content [13]. While most researchers believe that the best catalytic activity is obtained when WO 3 is highly dispersed on the surface of the catalyst, there has been some debate about this subject. It was shown that the catalyst has better catalyst activity with the WO 3 density of seven-eight atoms·nm −2 [14,15]. Many researchers have found that the addition of small amounts of metals such as Fe, Al, In, and Ga to Pt/WO 3 /ZrO 2 enhances catalysis and stability of n-heptane isomerization, and it was demonstrated that Cr can be used as a modifier in Pt/WO 3 /ZrO 2 catalysts. Based on economic considerations, Cr metal is a more cost-effective option, and is therefore a more suitable for industrial production than Ga metal [16][17][18]. In this work, n-heptane isomerization over Cr-promoted Pt/WO 3 /ZrO 2 was studied and compared to that over Pt/WO 3 /ZrO 2 . Results and Discussion Effect of Cr 2 O 3 Loading on Pt/ WO 3 /ZrO 2 Characterization of the CatalystsThe XRD patterns of Cr-Pt/WZ catalysts with different Cr loading ...

Mesoporous Ni–Cu/WOx/ZrO2 Catalyst with Highly Dispersed WOx Clusters: Efficient Catalysts for Selective Hydroisomerization of Isobutane to n-Butane

“…The specific surface areas (77.45 cm 3 /g) and pore size (9.74 nm) (listed in Table ) were slightly decreased for the deactivated catalyst, indicating that the deactivation of the 1Ni1Cu/mWZr-13 catalyst might be due to carbonaceous deposits covering the acidic sites and metal sites. The TG curves (shown in Figure S9) of the fresh and used 1Ni1Cu/mWZr-13 catalyst displayed a slight weight loss (0.17–0.21%) from 40 to 200 °C because of the free water evaporation and physically adsorbed water . The weight loss of the used 1Ni1Cu/mWZr-13 catalyst is 0.43%, and the fresh 1Ni1Cu/mWZr-13 catalyst has no weight loss in the region 380–600 °C.…”

“…The TG curves (shown in Figure S9) of the fresh and used 1Ni1Cu/ mWZr-13 catalyst displayed a slight weight loss (0.17−0.21%) from 40 to 200 °C because of the free water evaporation and physically adsorbed water. 17 The weight loss of the used 1Ni1Cu/mWZr-13 catalyst is 0.43%, and the fresh 1Ni1Cu/ mWZr-13 catalyst has no weight loss in the region 380−600 °C. The weight loss of the used 1Ni1Cu/mWZr-13 catalyst could be attributed to the carbonaceous deposits.…”

“…WO 3 /ZrO 2 -supported Pt (Pt/WO 3 /ZrO 2 ) showed good catalytic activity in the light alkane hydroisomerization at 200–260 °C. − However, Pt/WO 3 /ZrO 2 has the disadvantages of poison sensitivity, high cost, and deactivation at the reaction temperature.…”