Origin of Brönsted acidity in germanosilicates from neighboring Ge-hydroxyl groups

Constructing new Brönsted acid sites within zeolitic materials holds paramount importance for the advancement of solid-acid catalysis. Zeo-type germanosilicates, a class of metallosilicates with a neutral framework composed of tetravalent Ge and Si oxygen tetrahedrons, are conventionally considered not to generate Brönsted acid sites. Herein, we disclose an abnormal phenomenon with Ge-rich IWW-type germanosilicate (IWW-A) as an example that Ge-enriched germanosilicates are featured by mild Brönsted acidity. Using the art-of-state density functional theory calculation, ¹⁹F magic angle spinning nuclear magnetic resonance, microcalorimetric and ammonia infrared mass spectrometry- temperature-programmed desorption characterizations, the nature of germanosilicate's Brönsted acidity has been demonstrated to be closely related to the neighboring framework Ge-hydroxyl pairs. Besides, the contribution of Ge-OH groups to Brönsted acidity and the role of Ge-pair structure for maintaining mild acid strength have been elucidated. In catalytic cracking of n-hexane and methanol-to-olefins reaction, the IWW-A germanosilicate exhibit high light olefins selectivity, good recyclability and low carbon deposition, outperforming the benchmark zeolite catalyst, ZSM-5 aluminosilicate.