Several heterogeneous catalysts based on MCM-41 were synthesized either by chemical vapor deposition (CVD) or hydrothermally, i.e. adding SnCl 4 , SnCl 2 or ZnCl 2 as precursor salts into the MCM-41 synthesis gel. Synthesized materials were characterized by XRD, BET surface area, atomic absorption, UV-Vis, H 2-TPR, NH 3-TPD, TEM and pyridine-FTIR. Better textural properties and more reactive materials were obtained using tin salt precursors compared with ZnCl 2. UV-Vis and TPR analyses of selected Sn-MCM-41 materials indicate that depending on the synthesis and pretreatment conditions several species may be formed: Sn 4+ as Lewis acid sites of different coordination, SnO 2 nanoparticles and bulk tin oxide species. The presence of SnO 2 nanoparticles was also confirmed by TEM. Medium strength Lewis acid sites appear to increase nopol selectivity. Hydroxylated groups, i.e. Sn-OH, increased the weak acid sites and diminished nopol selectivity.

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The nopol rate model with ethyl acetate was the same that with toluene as solvent. Adsorption constants of compounds involved in the reaction were determined. Non-ideality of the liquid phase was related with the solvent solvation capacity. Solubility of formaldehyde in ethyl acetate was higher than in toluene.

h i g h l i g h t s " Kinetic model for nopol synthesis based on the Langmuir-Hinshelwood formalism is obtained. " The main product, nopol, inhibits the activity of the Sn-MCM-41. " The rate law is robust respect to equilibrium adsorption constants. " The effect of temperature on kinetic of nopol synthesis is mainly on the surface reaction constant.

Solid paraformaldehyde is a source of formaldehyde that is preferred when anhydrous conditions in chemical processes are required. In this contribution, several depolymerization models were proposed for paraformaldehyde in powder (PFP) and prills (PFS), and they were validated with experimental thermogravimetric analysis (TGA). For description of PFP depolymerization, a model of a single step was adequate, and for PFS the best model included two simultaneous mechanisms. Kinetic models were determined using Master Plot method; for PFS, small intervals of conversion were used in order to obtain the best model at each finite point of the progress of reaction. Apparent activation energies (E a ) were obtained by isoconversional methods. For PFP, E a was 31.7 kJ mol À1 and the model corresponded to Avrami-Erofeyev 2 (A2). For PFS decomposition, the activation energy of the two mechanisms was E a = 105.4 kJ mol À1 for a contracting volume (R3) model and E a = 48.4 kJ mol À1 for the Avrami-Erofeyev model.2015 Elsevier B.V. All rights reserved.