微量吸附量热技术研究Pd-Cu/SiO_2的表面吸附

Microcalorimetric Studies of Adsorption on the Surface of Pd-Cu/SiO_2

应用微量吸附量热技术研究了室温下 H2 ,CO,O2 和 C2 H4 在 m( Pd) /m( Si O2 ) =2 % ,m( Pd,Cu) /m( Si O2 ) [n( Pd) /n( Cu) =1 /1 ]=2 % ,m( Pd,Cu) /m( Si O2 ) [n( Pd) /n( Cu) =1 /4]=2 %和 m( Cu) /m( Si O2 ) =8%催化剂表面的吸附性能 ,并考察了 O2 对 C2 H4 吸附性能的影响 .结果表明 ,Pd-Cu/Si O2 具有与 Pd/Si O2数量相近的表面 Pd原子 .加入 Cu可使 Pd对 H2 和 CO的强吸附位数目相对减少 ,弱吸附位数目相对增加 .Pd增加了 H2 在 Cu/Si O2 催化剂表面的吸附量 ,加速了 O2 在 Cu表面的吸附速率 .Pd原子和 Cu原子在Pd-Cu/Si O2 中混合均匀且分散良好 .乙烯在 Pd/Si O2 表面吸附有乙川、 di-σ和π吸附态 .Cu的加入可抑制乙烯在 Pd表面解离吸附为乙川 ,促进了非解离的 di-σ和 π吸附态形成 .乙烯在室温下可与 Pd表面吸附氧发生氧化反应 ,加入 Cu可降低 Pd表面吸附氧的氧化活性 ,使乙烯在

Adsorption of H\-2, CO, O\-2 and C\-2H\-4 on \%m\%(Pd)/\%m\%(SiO\-2)=2%, \%m\%(Pd,Cu)/\%m\%(SiO\-2)\[\%n\%(Pd)/\{\%n\%(Cu)\}=1/1\]=2%, \%m\%(Pd,Cu)/\%m\%(SiO\-2)\[\%n\%(Pd)/\%n\%(Cu)=1/4\]=2% and \%m\%(Cu)/\%m\%(SiO\-2)=8%, catalysts was investigated by using the techniques of microcalorimetric adsorption at room temperature. The effect of O\-2 on adsorption of C\-2H\-4 on the surface of the catalysts was also studied. It is found that the number of sites for H\-2 adsorption on Pd\|Cu/SiO\-2 is close to that on Pd/SiO\-2. Addition of Cu decreases the sites of stronger adsorption and increases the sites of weaker adsorption of H\-2 and CO on Pd. On the other hand, Pd can promote the dispersion of Cu on SiO\-2 and accelerate the rate of O\-2 adsorption on Cu/SiO\-2. These results suggest that Pd and Cu atoms are well mixed and Pd atoms are well dispersed in the Pd\|Cu/SiO\-2 catalysts. Ethylene adsorbed on Pd/SiO\-2 produces ethylidyne and \%σ\% and di\|\%π\% species. The addition of Cu inhibits the formation of the dissociatively adsorbed species\_\_ethylidyne but promotes the formation of undissociatively adsorbed species\_\_\%π\% and di\|\%σ\% species for ethylene adsorption on Pd\|Cu/SiO\-2 catalysts. Ethylene may react with O\-2 adsorbed on Pd/SiO\-2 at room temperature. Cu decreases the activity of adsorbed O\-2 on Pd\|Cu/SiO\-2. Hence, ethylene may be activated effectively on Pd\|Cu catalysts.