tailieunhanh - phân tích eclectron trong hóa phân tích phần 3

Tham khảo tài liệu 'phân tích eclectron trong hóa phân tích phần 3', kỹ thuật - công nghệ, hoá học - dầu khí phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | impregnation technique used to prepare the alumina-containing catalysts was limited to a maximum support concentration of about 30 parts AI2O3 IOO parts Fe so a catalyst with high alumina concentration .e. 100 parts was not available for testing. Catalyst activity as measured by H2 CO conversion decreases as the support concentration increases. The Hj CO conversions obtained at 235 C at the two space velocities used in the tests are compared in Figure 5. The 8 parts SiO2 and the unsupported catalysts had the highest activities and on a per Fe basis gave essentially the same H2 CO conversions. The 8 parts AI2O3 catalyst also had high activity. The similarity in conversions for the unsupported and 8 parts supported catalysts show that the high activity is not due to surface areas alone. The very high potassium concentrations are responsible for the increase in catalyst activity over previous unsupported catalyst tests. While the BET surface areas of the SiOọ-contaixũng catalysts increase from 94 148 and 250 iriỊỊg at 8 25 and 100 parts SỈO2 IOO parts Fe the H2-Ì-CO conversions decrease at all conditions tested. The unsupported catalyst has a BET surface area of 38 TT Is-The increased BET surface areas are caused by the addition of High surface area support and do not necessarily reflect a large increased active metal surface area in the presence of a support. Our measurements Sect. of this report show that the fractional metal exposures for co reduced âlica-containing catalysts are the same as for unsupported with the same promoter concentrations thus crystallite size is constant. When alumina is added to the catalyst the exposure roughly doubles. Egiebor and Cooper 1985 measured the BET surface areas of both fresh and used silica supported catalysts with compositions of 100 Fe Cu K with 21 50 and 73 parts SiO2. Prior to use these catalysts had surface areas of 151 252 and 275 rrp g which agree with our values but after use the surface areas decreased .