Alcohol Dehydration Reactions as Chemical Precursors for Coke

Alcohol Dehydration Reactions as Chemical Precursors for Coke Formation and Acidity Probes in Tungstated Zirconia Catalysts 

Gustavo Larsen. Edgar Lotero, Mark Nabity, Lucia Petkovic and Carlos A. Querini  

The temperature-programmed desorption of low-molecular weight alcohols was studied over tungstated zirconia and acidic zeolites. Tungstated zirconia (WZ) acids have less tendency to deactivate due to carbon deposition and to form oligomeric products. Proton exchange is also less important in WZ.  

Tungstated zirconia (WZ) catalysts have been proposed as viable candidates for alkane isomerizations, especially those heavier than C4 [1]. In this work, alcohol dehydrations were used to rank the acidity of WZ with respect to that of HY zeolite, and to evaluate the ability of these catalysts to resist coking during a reaction that yields an olefin molecule as the primary product. The results from temperature-programmed reaction and infrared spectroscopy studies allowed us to gain some insight into the relative stability of WZ. 

The alcohols used were 1-propanol and tert-butanol (with and without deuteration of the hydroxyl group) from Aldrich . The preparation of WZ (W content 6 wt%) is described elsewhere [2]. In brief, the catalyst is obtained by aqueous incipient wetness impregnation of hydrous zirconia with a solution containing the appropriate amount of ammonium metatungstate. The sample is subsequently calcined at 1096 K for one hour under flowing air. EXAFS measurements carried out at the National Synchrotron Light Source [7] showed that the WZ sample has an average W-O coordination number and distance of 4.7 and 1.69 A respectively. The surface area of the calcined material is 36 m /g. XRD reveals that a small amount of monoclinic zirconia was formed upon calcination. The Y-zeolite catalyst was 

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