Inorganic Chemistry and Catalysis Group, Department of Chemistry, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht, The Netherlands.
Chemistry. 2012 Jan 23;18(4):1094-101. doi: 10.1002/chem.201102949. Epub 2011 Dec 9.
A time-resolved in situ micro-spectroscopic approach has been used to investigate the Brønsted acidic properties of fluid-catalytic-cracking (FCC) catalysts at the single particle level by applying the acid-catalysed styrene oligomerisation probe reaction. The reactivity of individual FCC components (zeolite, clay, alumina and silica) was monitored by UV/Vis micro-spectroscopy and showed that only clay and zeolites (Y and ZSM-5) contain Brønsted acid sites that are strong enough to catalyse the conversion of 4-fluorostyrene into carbocationic species. By applying the same approach to complete FCC catalyst particles, it has been found that the fingerprint of the zeolitic UV/Vis spectra is clearly recognisable. This almost exclusive zeolitic activity is confirmed by the fact that hardly any reactivity is observed for FCC particles that contain no zeolite. Confocal fluorescence microscopy images of FCC catalyst particles reveal inhomogeneously distributed micron-sized zeolite domains with a highly fluorescent signal upon reaction. By examining laboratory deactivated FCC catalyst particles in a statistical approach, a clear trend of decreasing fluorescence intensity, and thus Brønsted acidity, of the zeolite domains is observed with increasing severity of the deactivation method. By comparing the average fluorescence intensities obtained with two styrenes that differ in reactivity, it has been found that the Brønsted acid site strength within FCC catalyst particles containing ZSM-5 is more uniform than within those containing zeolite Y, as confirmed with temperature-programmed desorption of ammonia.
已经使用时间分辨原位微光谱方法，通过应用酸催化的苯乙烯齐聚探针反应，在单颗粒水平上研究了流化催化裂化（FCC）催化剂的布朗斯台德酸性。通过紫外/可见微光谱监测个别 FCC 成分（沸石、粘土、氧化铝和二氧化硅）的反应性，表明只有粘土和沸石（Y 和 ZSM-5）含有足够强的布朗斯台德酸位，可催化 4-氟苯乙烯转化为碳阳离子物种。通过将相同的方法应用于完整的 FCC 催化剂颗粒，发现沸石的紫外/可见光谱的指纹明显可辨。事实上，对于不含沸石的 FCC 颗粒几乎观察不到反应性，这证实了沸石的这种几乎排他性的活性。通过共焦荧光显微镜观察 FCC 催化剂颗粒的图像，发现反应后沸石域呈现出不均匀分布的微米级尺寸，并具有高度荧光信号。通过以统计方式检查实验室失活的 FCC 催化剂颗粒，观察到沸石域的荧光强度（因此布朗斯台德酸度）随失活方法的严重程度的增加而明显降低。通过比较两种在反应性上有所不同的苯乙烯的平均荧光强度，发现含有 ZSM-5 的 FCC 催化剂颗粒中的布朗斯台德酸位强度比含有沸石 Y 的更均匀，这与氨的程序升温脱附得到了证实。
