Effect of supports on the catalytic performance of Pt/WO3-ZrO2 catalysts for hydroisomerization
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摘要: 以平衡吸附过氧钨酸的水合氧化锆为前驱体，经焙烧得到WO3-ZrO2固体酸，并采用XRD、UV-vis、NH3-TPD等手段考察了过氧钨酸吸附液浓度及焙烧温度对WO3-ZrO2固体酸组成、结构及酸性的影响。通过BET、H2-TPR、H2-TPD等表征手段和正戊烷临氢异构反应，考察了负载铂后相应催化剂的结构、还原与氢吸附性质及其催化正戊烷临氢异构反应的性能。结果表明，焙烧温度为700℃时，随着吸附液浓度的增加，所得载体酸度及相应催化剂比表面积均先增加后减小，且在吸附液浓度为82 mmol W/L时达到最大值。吸附液浓度为59 mmol W/L时，随着焙烧温度的升高，所得载体四方相氧化锆含量、酸度及相应催化剂比表面积均降低。吸附液浓度为82 mmol W/L、焙烧温度为700℃所得载体负载0.5%（质量分数）铂后催化活性最高。该催化剂在250℃常压临氢操作、n（H2）/n（n-C5H12）为3、WHSV为1.0 h-1的条件下，催化正戊烷异构反应中异戊烷收率可达57.7%。
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关键词:
- Pt/WO3-ZrO2 /
- 平衡吸附 /
- 正戊烷 /
- 临氢异构
Abstract: A series of WO3-ZrO2 solid acids were synthesized by calcining the equilibrium adsorbed peroxotungstic acid/hydrated zirconia precursors. The influences of peroxotungstic acid concentration and calcination temperature on the composition, structure and acidity of the obtained solid acids were evaluated by using XRD, UV-vis and NH3-TPD. Pt/WO3-ZrO2 catalysts were prepared by impregnation method and characterized by BET, H2-TPR and H2-TPD. The catalytic performance in the hydroisomerization of n-pentane was investigated. It was found that under the same calcination temperature, both the support acidity and the catalyst surface area first increase and then decrease with the increase of peroxotungstic acid concentration, and are maximized when the peroxotungstic acid concentration reaches 82 mmol W/L. When the peroxotungstic acid possesses the same concentration of 59 mmol W/L, the tetragonal zirconia fraction, support acidity and the catalyst surface area decrease with the increase of calcination temperature. When the peroxotungstic acid concentration and the calcination temperature of the support are 82 mmol W/L and 700℃ respectively, the obtained catalyst shows the best catalytic performance. The yield of isopentane reaches 57.7% under the reaction condition of ambient pressure, 250℃, n(H2)/n(n-C5H12)=3 and WHSV=1.0 h-1.-
Key words:
- Pt/WO3-ZrO2 /
- equilibrium adsorption /
- n-pentane /
- hydroisomerization
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图 2 不同过氧钨酸吸附液浓度 (a) 及焙烧温度 (b) 所得WO3-ZrO2载体的E~[F(R∞) ·E]1/2曲线
Figure 2 E~[F(R∞) ·E]1/2 curves of WO3-ZrO2 supports with different peroxotungstic acid concentration (a) and calcination temperature (b)
NC: not calcined
图 5 Pt/WO3-ZrO2催化剂催化正戊烷临氢异构反应所得异戊烷收率
Figure 5 Isopentane yields of n-pentane hydroisomerization reactions catalysed by Pt/WO3-ZrO2 reaction condition: atmospheric pressure, 250℃, n(H2)/n(n-C5H12)=3, WHSV=1.0 h-1
表 1 WO3-ZrO2载体中四方相氧化锆的体积分数
Table 1 Volume fractions of tetragonal zirconia in WO3-ZrO2 supports
Support Vt /% WZ (23, 700) 17 WZ (59, 700) 97 WZ (82, 700) 100 WZ (108, 700) 100 WZ (185, 700) 100 WZ (59, 800) 22 WZ (59, 900) 6.5 
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表 2 WO3-ZrO2载体的酸位分布
Table 2 Acid distribution data of WO3-ZrO2 supports
Support Acid amount w/(μmol·g-1)/Temperature t/℃ Total acid amount w/(μmol·g-1) peak 1 peak 2 peak 3 WZ (23, 700) 36/175 69/240 178/363 283 WZ (59, 700) 55/174 89/231 166/318 310 WZ (82, 700) 74/176 162/243 244/329 480 WZ (108, 700) 71/177 134/239 212/326 417 WZ (185, 700) 69/175 135/234 258/326 461 WZ (59, 800) 54/170 87/228 160/323 301 WZ (59, 900) 34/168 53/223 85/317 171
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表 3 Pt/WO3-ZrO2催化剂的比表面积与孔结构
Table 3 Surface area and porosity data of Pt/WO3-ZrO2 catalysts
Catalyst Surface area A/(m2·g-1) Pore size d/nm Pore volume v/(cm3·g-1) Pt/WZ (23, 700) 44.1 12.3 0.17 Pt/WZ (59, 700) 67.4 7.9 0.19 Pt/WZ (82, 700) 79.6 6.6 0.19 Pt/WZ (108, 700) 72.6 5.6 0.13 Pt/WZ (185, 700) 70.5 7.9 0.18 Pt/WZ (59, 800) 50.7 6.9 0.21 Pt/WZ (59, 900) 23.0 17.1 0.11
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