A fast method for determination of surface area of zeolite-based catalysts and zeolites using near infrared emission spectroscopy

Abstract

A new, fast and reagent-free method for determination of the surface area of zeolite-based catalysts and zeolites using direct spectral information from near infrared emission spectroscopy and chemometrics is described. Small sample amounts (approximately 3.0 mg) were heated at a fixed temperature (270 °C) and their emission spectra recorded using a prototype emission spectrometer with an acousto-optical tunable filter as a wavelength selector. Emission spectra were correlated with the surface area determined by the reference Brunauer–Emmett–Teller (BET) method, using Partial Least Squares (PLS) regression models. Sixty-six samples of Y zeolite-based catalysts, ZSM-5 zeolite-based catalysts and Y and ZSM-5 zeolites were used to construct the models. A local model (including only catalysts) and a global model (including catalysts and zeolites) were developed with an RMSEP of 24.7 and 22.3 m² g⁻¹, respectively (which represents 9% and 8% of the median value, respectively) and precision (repeatability) of 26.0 m² g⁻¹. A paired t-test at the 95% confidence level demonstrated that the analytical results obtained from NIRES multivariate models are equivalent to measurements performed by the BET method. The cost and speed were improved in comparison with the BET method. The method based on NIRES requires no sample preparation and speeds up the surface area analysis (4.5 min) about 370 times when compared with the BET method.