乙苯脱氢与逆水煤气变换偶合反应的铁/活性炭催化剂研究

Study of Fe/AC Catalysts for the Coupling of Dehydrogenation of Ethylbenzene with Reversed Water Gas Shift Reaction

研究了活性炭负载的Ｆｅ 催化剂在乙苯脱氢与逆水煤气变换偶合反应中的催化活性，考察了催化剂中的铁物相，添加Ｌｉ， Ｎａ 和Ｋ 等碱金属以及ＣＯ２ 对催化活性的影响． 实验表明，Ｆｅ３Ｏ４ 可能是偶合反应的活性相． 在ＣＯ２气氛中，适当还原度的、经碱金属元素调变后的Ｆｅ／ＡＣ的催化活性较好，苯乙烯的选择性明显提高． 以ＮＨ３ 和ＣＯ２为探针分子，运用微分吸附量热技术表征了催化剂的表面酸碱性质． 结果表明，活性炭表面具有较多的弱酸位． 担载铁后，ＮＨ３ 的起始吸附热为９６ ｋＪ／ｍｏｌ， 吸附饱和覆盖度为１１２ μｍｏｌ／ｇ， 说明Ｆｅ／ＡＣ表面具有酸性；ＣＯ２ 的起始吸附热为７２ ｋＪ／ｍｏｌ， 吸附饱和覆盖度为７ μｍｏｌ／ｇ， 表明催化剂表面也有少量的碱位． 碱金属元素的加入减弱了Ｆｅ／ＡＣ催化剂表面上的酸强度，同时产生了一定量的碱性位，因而显著提高了苯乙烯的选择性．ＣＯ２ 的作用是及时除去脱氢反应产生的Ｈ２ ， 促进乙苯脱氢生成苯乙烯，并抑制乙苯的加氢裂解．

The coupling of the reaction of dehydrogenation of ethylbenzene (EB) to styrene (STY) with the reversed water gas shift reaction (RWGSR) has been studied over activated carbon (AC) supported Fe catalysts at 600 ℃ and atmospheric pressure. Reaction evaluation reveals that Fe 3O 4 may be the active phase for the coupling reaction. The catalytic activity of the catalysts is correlated to their surface acidity and basicity, as determined by microcalorimetric adsorption of NH 3 and CO 2. It is found that the AC itself possesses little acidity and basicity while the Fe/AC catalyst displays moderate acidity and weak basicity. Upon the addition of Li, Na and K, the basicity increases while the acidity decreases significantly on the surface of the Fe/AC catalysts. Accordingly, the alkali metal modified Fe/AC catalysts exhibit higher selectivity for the reaction of EB+CO 2→STY+CO+H 2O. The interaction of CO 2 with the basic sites in the catalysts promotes the RWGSR, causing the effective removal of the hydrogen produced by the dehydrogenation of EB and enhancing the dehydrogenation of EB to produce STY. In addition, the decrease of acidity on the catalysts and H 2 concentration in the reaction atmosphere depresses the cracking of EB to form toluene and benzene, further increasing the selectivity for the reaction to STY.