This article reports the use of combined techniques (thermal desorption and spectroscopic analysis) for the characterization of Brønsted sites in microporous solid catalysts. The specific aim was to provide a quantitative determination of sites with slightly different acidities in chabazite-related silicoaluminophosphate (SAPO) materials, which display three bridged hydroxyls, OH A , OH B , and OH C , absorbing at 3630, 3614, and 3600 cm -1 , respectively. To this aim, different approaches were employed. First, the total concentration of Brønsted sites was calculated by classical NH 3 -TPD experiments. Ammonia was preferred to pyridine due to the small kinetic diameter, allowing easy access and diffusion inside the small cavities of chabazite. Second, FTIR spectroscopy was employed to study the adsorption of NH 3 and CO. The Lambert-Beer equation, using extinction coefficients from the literature, was employed to estimate the total amount of Brønsted sites involved in the formation of NH 4 + ammonium ions or in CO/H + adducts. The agreement among the data obtained by the three methods, which is excellent, is discussed critically. The fraction of each acid group in samples with different Brønsted site densities and strength distributions was determined with great accuracy. This finally allowed calculation of the extinction coefficients of the three hydroxyls of the H-SAPO-34 catalysts, which were A ) B ) 3.9 cm µmol -1 and C ) 6.0 cm µmol -1 . It is proposed that these values are of general use for determining the distribution of acid sites of SAPOs and zeolites whose hydroxyls absorb in the same range of wavenumbers.
As functional near-infrared spectroscopy (fNIRS) is developed as a neuroimaging technique and becomes an option to study a variety of populations and tasks, the reproducibility of the fNIRS signal is still subject of debate. By performing test-retest protocols over different functional tasks, several studies agree that the fNIRS signal is reproducible over group analysis, but the inter-subject and within-subject reproducibility is poor. The high variability at the first statistical level is often attributed to global systemic physiology. In the present work, we revisited the reproducibility of the fNIRS signal during a finger-tapping task across multiple sessions on the same and different days. We expanded on previous studies by hypothesizing that the lack of spatial information of the optodes contributes to the low reproducibility in fNIRS, and we incorporated a realtime neuronavigation protocol to provide accurate cortical localization of the optodes. Our proposed approach was validated in 10 healthy volunteers, and our results suggest that the addition of neuronavigation can increase the within-subject reproducibility of the fNIRS data, particularly in the region of interest. Unlike traditional approaches to positioning the optodes, in which low intra-subject reproducibility has been found, we were able to obtain consistent and robust activation of the contralateral primary motor cortex at the intra-subject level using a neuronavigation protocol. Overall, our findings support the hypothesis that at least part of the variability in fNIRS cannot be only attributed to global systemic physiology. The use of neuronavigation to guide probe positioning, as proposed in this work, has impacts to longitudinal protocols performed with fNIRS.
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