Mixed Ba 1−x La x F 2+x fluoride materials as catalyst for the gas phase fluorination of 2-chloropyridine by HF

The stability under different atmospheres (dry or wet nitrogen or air, HF, reaction medium) and the catalytic performances of BaF 2 -LaF 3 based catalysts for the fluorination of 2-choropyridine by Cl/F exchange with HF as fluorinating agent were investigated. Thermal decomposition of metal trifluoroacetate and precipitation from nitrate precursor methods were used as synthesis methods. Depending on the synthesis method and the La/La + Ba molar ratio (x), an intimate mixture of BaF 2 and LaF 3 metal fluorides or a Ba 1−x La x F 2+x mixed metal fluoride with high specific surface area were formed. In comparison with BaF 2 , the mixed metal fluorides led to higher specific surface areas and prevented the sintering phenomenon observed under wet atmosphere which led to a significant decrease of the specific surface area. Moreover, Ba 1−x La x F 2+x catalysts had not evolved under the fluorination reaction contrary to BaF 2 for which a stable BaF 2−x Cl x material (with x close to 0.8) was formed by reaction with the by-product HCl. The turn over frequency (TOF) was similar for all barium based catalysts for the fluorination of 2-chloropyridine. Nevertheless, among the studied materials, Ba 0.5 La 0.5 F 2.5 was the most promising catalyst for the transformation of 2-chloropyridine due to high activity (related to its high specific surface area and its moderate strength of Lewis acidity) and high stability.