Increasing the Bronsted Acidity of Flame-Derived Silica/Alumina up to Zeolitic Strength
Increasing the Bronsted Acidity of Flame-Derived Silica/Alumina up to Zeolitic Strength
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DOI：
10.1002/anie.201003391
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发表时间：
2010-01-01
影响因子：
16.6
通讯作者：
Baiker, Alfons
中科院分区：
文献类型：
--
作者：
Huang, Jun;van Vegten, Niels;Baiker, Alfons
固体酸有助于更清洁和更容易的反应，因此在许多催化应用中取代了有毒，腐蚀性和不可回收的液体矿物酸，最突出的是将10亿吨原油裂化和精炼成有用的化学成分。[1，2]对于当前涉及能源和环境友好工艺的全球挑战，[3，4]化学家和工程师致力于设计改进的固体酸，因为它们在可再生燃料生产和清洁化学工艺中的应用中起主导作用。[2，5，6]所需的固体酸应具有可调的性质，以提供最佳的酸度，用于目标反应的有效催化。无定形二氧化硅/氧化铝（SA）是一种流行的固体酸，其提供中等的布朗斯台德酸度，尽管比沸石的酸度弱。[7]SA已被直接用作炼油厂中重要的酸催化剂，并且还被用作许多氢化和氧化反应中的纳米颗粒的优异载体。[8]目前的努力旨在提高SA的布朗斯台德酸性，使得它们在强度上接近或理想地类似于沸石的强度。[9-12]在此，我们表明通过火焰喷雾热解（FSP SA）制备的SA表现出类似于沸石的强布朗斯特酸性。发现FSP SA中的一些Brønsted酸中心甚至比被认为是最强酸性的沸石H-ZSM-5的Brønsted酸中心更强，SA的Brønsted酸性是由相邻的铝和硅醇基团产生的。然而，现有的制备方法，如接枝，接枝，共沉淀和水解，导致的SA的不均匀的组成，阻碍了其酸性的增强。在这些方法中，通常需要控制pH值和高温煅烧，以使铝和硅在整个相或网络中扩散。[13]FSP允许在一个步骤中生产热稳定的纳米颗粒，目前已经完成了中试规模的反应，接近500ghn_1的生产率，从而显示出工业应用的潜力。[14]FSP允许
Solid acids facilitate cleaner and much easier reactions and thus have replaced toxic, corrosive, and unrecyclable liquid mineral acids in many catalytic applications, the most prominent being the cracking and refining of a billion tons of crude oil into useful chemical components.[1, 2] For current global challenges involving energy sources and environmentally friendly processes,[3, 4] chemists and engineers strive towards designing improved solid acids because of their dominant role in renewable fuels generation and application in clean chemical processes.[2, 5, 6] The desired solid acids should have tunable properties to offer optimal acidity for efficient catalysis of the target reactions. Amorphous silica/alumina (SA) is one of the popular solid acids that provide moderate Brønsted acidity, albeit weaker than that of zeolites.[7] SAs have been directly used as an important acid catalyst in oil refineries and, furthermore, have been applied as excellent supports for nanoparticles in many hydrogenation and oxidation reactions.[8] Current efforts are aimed at enhancing the Brønsted acidity of SAs so that they are close or ideally similar in strength to that of zeolites.[9–12] Herein, we show that SAs prepared by flame-spray pyrolysis (FSP SAs) exhibit a strong Brønsted acidity resembling that of zeolites. Some Brønsted acid sites in the FSP SAs were found to be even stronger than those of H-ZSM-5, which is regarded as the most acidic zeolite.Brønsted acidity of SAs is generated by having neighboring aluminum and silanol groups. However, inhomogeneous composition of the SAs resulting from existing preparation methods, such as cogelation, grafting, co-precipitation, and hydrolysis, hinder enhancement of their acidity. Control over pHvalues and high temperature calcinations are often required in these methods for the diffusion of aluminum and silicon throughout the phase or network.[13] FSP allows production of thermally stable nanoparticles in a single step, and currently pilot-plant-scale reactions have been accomplished, approaching a production rate of 500ghÀ1, thus showing potential for industrial applications.[14] FSP allows