Cu/SiO2 catalysts for methanol to methyl formate dehydrogenation - A comparative study using different preparation techniques

A comparative study of the different preparation conditions required to pro duce supported copper catalysts by the wet impregnation (VIII) and the ion- exchange (IE) methods has been carried out. Two silicas with different text ural characteristics, and one form of naturally occurring pumice were used as supports. In order to obtain specific chemical species of copper in solu tion as well as different support reactivities, three different pH values ( 1, 4.5 and 1 1.5) for the impregnating solution were tested, The catalysts were characterized by means of different techniques, such as XFS, BET, TPR, dissociative chemisorption of N2O, XRD, TEM. EXAFS and XANES and methanol (MeOH) dehydrogenation. The use of copper solutions with high pH, especiall y after several hours of contact with the chosen carrier, with high solutio n volume to pore volume ratios, modifies strongly the support texture decre asing the: specific surface areas (SSA) of the final catalyst, Copper parti cle sizes lower than a critical limit, or that did not fulfill a certain en semble requirement, were not active for methanol dehydrogenation indicating that below such limit, this might be a structure-sensitive reaction. A cat alyst (WI-11A) prepared by a simple incipient wetness impregnation method a t an alkaline pH similar to that used for the IE technique, showed high dis persion and it was simply activated under reaction conditions (MeOH/N-2, 23 0 degreesC) giving conversions around 50% and selectivities to methyl forma te (MF) in the order of 75-80% with no deactivation observed after 3 h of t ime on stream. (C) 2000 Elsevier Science B,V. All rights reserved.