Rapid determination and classification of zeolites based on Si/Al ratio using FTIR spectroscopy and chemometrics

Abstract

The aim of this study was to develop fast and facile methods for the determination and classification of zeolite samples based on Si/Al ratio by fourier transform infrared spectroscopy (FTIR). The ZSM-5, ZSM-48 and mordenite catalysts spectral data were used for estimation of Si/Al ratio using two approaches according to PLS-R and SVM-R algorithms in whole (600–4000 cm−1) and fingerprint (3000–3800 cm−1) spectral regions. The drift-FTIR spectral data were also analyzed by classification method using the soft independent modelling of class analogies (SIMCA) for mordenite, ZSM-5 and ZSM-48 catalysts classification. Performance of the regression models was adequate with good statistical results. The correlation coefficients (R2) were about 0.99 and 0.96 for SVM and PLS regression models. The results obtained for the SVM model of the MIR spectra was very good and encouraging, since the RMSEP was low (6%) and the quantitative results were in accordance with X-ray fluorescence analysis. Then the samples were classified into three mordenite, ZSM-5 and ZSM-48 classes based on their Si/Al ratio by the SIMCA method using raw and pre-treated spectra. Using SIMCA technique, the 100% of samples were correctly classified in pre-treated spectra. The accurate and stable model was obtained with pre-treated spectra for SIMCA model (100% of sensitivity and 100% of specificity). The results indicated that drift-FTIR spectroscopy in conjunction with multivariate calibration and classification methods is a fast and reliable methodology that can be easily implemented for determination and classification of zeolite catalysts based on their Si/Al ratio.