负载铂催化剂中沸石载体酸性对甲烷两步转化的影响

考察了具有相同金属分散度的Pt/NaY、Pt/HNaY、 Pt/HY、Pt/NaBeta和Pt/HBeta催化剂中沸石载体的酸性对在低温下（≤250 ℃）甲烷两步等温转化反应以及由甲烷解离吸附产生的表面碳物种分布的影响。由甲烷等温两步转化生成的C2+烃类产物的总量随着载体酸性的增加而明显增加；C2～C6产物的分布也发生了变化。由表面碳物种的程序升温加氢结果表明，在各种催化剂上碳物种的形式是相似的，其总量和具有活性的Cα物种的量均因载体酸性增加而增加，反应性也增大。这种因沸石载体酸性变化而引起的载体效应是由金属和载体的相互作用造成负载在酸性载体上铂粒子的贫电子性而引起，即由金属粒子电子性质的变化而引起的催化性质的变化。

Effect of zeolite acidity on two-step conversion of methane over supported platinum catalysts

The platinum catalysts supported on two series of supports (NaY, HNaY, HY and NaBeta, HBeta) were prepared to study the influence of electronic properties of platinum particles on two-step, isothermal conversion of methane to higher hydrocarbons after correcting the effect of particle size. The activity of catalysts, that is, the total amount of methane converted to C2+ hydrocarbons and the distribution of C2～C6 products were investigated in the catalytic reaction for methane conversion over platinum catalysts supported on Y and Beta zeolites with different acidity. The results showed that the activity of catalyst increased with increasing support acidity and the selectivity to C2～C6 products varied with support acidity. Moreover, the distribution and reactivity of surface carbonaceous species (CHx) chemisorbed on the catalysts, generating from the methane decomposition at first step were characterized by temperature-programmed hydrogenation (TPH). The total amounts of CHx (Cα+Cβ) and the Cα species, most of which is known to give C2+ hydrocarbons on hydrogenation and which is main resource of C2+ hydrocarbon products increased when the acidity of support increased; The reactivity of surface carbon was enhanced on acidic support compared to neutral support. The changes of catalytic properties are due to electron deficient nature of platinum particles on acidic support from the interaction of metal and support.