Methanol Synthesis and Decomposition Reactions Catalyzed by a Model Catalyst Developed from Bis(1,5-diphenyl-1,3,5-pentanetrionato)dicopper(II)/Silica
Autor: | Mark G. White, William P. Henry, Samantha A. Ranaweera |
---|---|
Jazyk: | angličtina |
Rok vydání: | 2017 |
Předmět: |
General Chemical Engineering
Inorganic chemistry Batch reactor chemistry.chemical_element 02 engineering and technology General Chemistry 010402 general chemistry 021001 nanoscience & nanotechnology 01 natural sciences Chemical synthesis Copper Article 0104 chemical sciences Catalysis Metal lcsh:Chemistry chemistry.chemical_compound Reaction rate constant chemistry lcsh:QD1-999 visual_art visual_art.visual_art_medium Methanol 0210 nano-technology Chemical decomposition |
Zdroj: | ACS Omega, Vol 2, Iss 9, Pp 5949-5961 (2017) ACS Omega |
ISSN: | 2470-1343 |
Popis: | Silica-supported model copper catalysts were prepared by supporting bis(1,5-diphenyl-1,3,5-pentanetrionato)dicopper(II), Cu2(dba)2, on Cab-O-Sil by a batch impregnation technique. This metal complex showed a strong affinity for the silica support, developing monolayer coverages near the value predicted from a consideration of the size and shape of the planar metal complex (2.6 wt % Cu). The supported catalysts were subsequently activated by decomposing the organic ligands at 400 °C in air followed by reduction with 2% H2/He at 250 °C. One sample was prepared having a loading of 3.70 wt % Cu2(dba)2/silica catalyst, and it was examined for the methanol synthesis reaction under the following conditions: 250 °C with an equimolar gas mixture of CO and H2 in a high-pressure batch reactor. Kinetic data over the model catalyst were fit to a rate equation, second order in the limiting reactant (H2), with a pseudo-second-order rate constant k2[CO]o[H2]o = 0.0957 [h-g total Cu]−1. A control experiment using a commercial catalyst, Cu/ZnO/Al2O3 with a copper loading of 41.20 wt %, showed a value of k2[CO]o[H2]o = 0.793 [h-g total Cu]−1. A fresh sample of Cu2(dba)2/silica was examined for methanol decomposition reaction at 220 °C. The model catalyst shows a methanol decomposition first-order rate constant greater than that of the commercial Cu/ZnO/Al2O3catalyst: 1.59 × 10–1 [min-g total Cu]−1 versus 9.6 × 10–3 [min-g total Cu]−1. X-ray diffraction analyzes confirm the presence of CuO particles in both catalysts after calcinations. Copper metal particles were found in both catalysts (fractional Cu dispersions were 0.11 and 0.16 on commercial and model catalysts, respectively) after the reduced catalysts were used in both the methanol synthesis and decomposition reactions. Using the values of copper dispersion found in these samples, we recalculated the rate constants for the two reactions per unit surface copper. These refined rate constants showed the same trends as those reported per total amount of Cu. One role of the promoter(s) in the commercial catalyst is the inhibition of the methanol decomposition reaction, thus allowing higher MeOH synthesis reaction rates in those regimes not controlled by thermodynamics. |
Databáze: | OpenAIRE |
Externí odkaz: |