Abstract
Raman spectroscopy was used for the quantitative determination of Mo and W in Mo- and W-supported mesoporous silica (Mo/SBA-15 and W/SBA-15, respectively) and Mo-supported beta zeolite (Mo-BEA). Three Raman quantitative models were developed and optimized for the metal contents of Mo/SBA-15, W/SBA-15, and Mo/BEA. Subsequently, the models were characterized using the root mean square error of calibration (RMSEC), root mean square error of cross-validation (RMSECV), root mean square error of prediction (RMSEP), correlation coefficient, and predicted residual error sum of squares (PRESS) diagnostic function. The calibration range of the models were in the range of approximately 2–40 wt% for the SBA-15 support and 1–21 wt% for the BEA support because the BEA support presented lower Mo absorption than the SBA-15 support. The RMSEC, RMSECV, and RMSEP values were below 1.80% for all developed models. The highest and lowest correlation coefficients corresponded to the W/SBA-15 (0.9984) and Mo/BEA (0.9777) models, respectively. The change in catalyst support affected the mentioned chemometric parameters (Mo/SBA-15 vs. Mo/BEA). Subsequently, Raman spectroscopy combined with the temperature control stage was used to study the calcination of Mo/BEA, Mo/SBA-15, and W/SBA-15 using three-dimensional diagrams, in which the changes in catalyst structure were analyzed as functions of the temperature and time. Raman spectroscopy was determined to be a suitable analytical tool for the quantitative analysis of the metal contents of the catalyst and optimization of the calcination process. Therefore, Raman spectroscopy can be used during catalyst manufacturing.
Highlights
During the quality control step, which is the last step of production processes and includes quantitative and qualitative evaluation, it is determined whether the final product meets consumers’demands
The Mo/SBA-15 catalysts were synthesized via the impregnation of ammonia heptamolybdate (AHM) on SBA-15 followed by calcination, when the O=Mo=O bonds were formed
AHM decomposed to molybdenum (VI) oxide (MoO3 ) and stronger bonds were formed between the Mo atoms and support
Summary
During the quality control step, which is the last step of production processes and includes quantitative and qualitative evaluation, it is determined whether the final product meets consumers’demands. The production and processing of chemical catalysts are not significantly different from other production processes, and quality control determines the applicability of the final products. The catalysts must meet a number of chemical and physical properties that are determined based on ASTM standards. Analytical methods such as potentiometric titration, wet chemistry, and especially methods for determining metal content are used to determine the chemical composition. The analytical methods used to control the metal contents of catalysts, such as X-ray fluorescence, inductively coupled plasma optical emission spectroscopy (ICP-OES), and atomic absorption spectroscopy, are time-consuming, expensive, and limited by parameters such as the state
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