Evolution of strong acidity and high-alkane-cracking activity in ammonium-treated USY zeolites
Evolution of strong acidity and high-alkane-cracking activity in ammonium-treated USY zeolites
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DOI：
10.1016/j.apcata.2011.07.007
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发表时间：
2011-10
影响因子：
5.5
通讯作者：
K. Okumura;Takuya Tomiyama;Nami Morishita;T. Sanada;Kazuhiro Kamiguchi;N. Katada;M. Niwa
中科院分区：
文献类型：
--
作者：
K. Okumura;Takuya Tomiyama;Nami Morishita;T. Sanada;Kazuhiro Kamiguchi;N. Katada;M. Niwa
用硝酸铵溶液处理由NH_4-Y沸石水蒸汽处理制备的USY沸石。用硝酸铵溶液处理导致USY沸石的辛烷裂解活性的显著增强。通过红外/质谱-程序升温脱附（IRMS-TPD）研究发现，所制备的USY分子筛具有足够强的酸性，可以催化烷烃裂解。在超稳Y上的酸强度（ΔH）值约为0.001。150kJmol−1。在Y型分子筛催化下，烷烃裂解反应的活化能与ΔH呈线性关系。正辛烷和正己烷在不同类型FAU分子筛上的吸附热几乎不变。这意味着酸中心的强度越高，烷烃裂解的本征活化能越小。该研究清楚地表明，用NH 4+处理是在USY沸石中产生非常强的酸性的关键。此外，铵处理的USY沸石的高催化活性的起源归因于强酸性的演变，而不是在烷烃的吸附能的变化，基于酸强度，烷烃吸附热，和活化能的测量。
USY zeolites prepared by steam treatment of NH4-Y zeolites were treated with ammonium nitrate solutions. Treatment with ammonium nitrate solutions resulted in a significant enhancement of the octane-cracking activity of the USY zeolites. We found by infrared spectroscopy/mass spectrometry-temperature programmed desorption (IRMS-TPD) of NH3that the prepared USY zeolites have acidity strong enough to catalyze alkane cracking. The acid strength (ΔH) values of the enhanced Brønsted OH on the USY are found to be ca. 150kJmol−1. A linear correlation between ΔH and the activation energy in alkane cracking was obtained when Y-type zeolites were used for the reaction. The heats of adsorption of octane and hexane were almost constant over various types of FAU zeolites. This means that the higher the strength of the acid site, the smaller the intrinsic activation energy of the alkane cracking. This study clearly indicated that treatment with NH4+was the key to creating very strong acidity in USY zeolites. Furthermore, the origin of the high catalytic activity of the ammonium-treated USY zeolites was attributed to the evolution of strong acidity rather than changes in the adsorption energies of the alkanes, based on the measurements of acid strength, heat of alkane adsorption, and activation energy.