Synthesis and characterization of acid silver salts of 12-tungstophosphoric acid

• Acid Ag salts of WPA are between WPA salts with small and large metal ions.
• Salts has a cubic structure, with the ratio I[1 1 0]/I[2 2 2] that decreases with Ag%.
• XRD showed that acid salts are two-phase mixtures of neutral Ag salt and WPA.
• Ag salts are less effective but more stable catalysts for EtOH dehydration than WPA.
• Activity decreases but selectivity for ethylene and diethyl ether rises with Ag%.

The silver acid salts AgxH3−xPW12O40 (AgxWPA), where Ag content is x = 1 up to x = 2.5, were synthesized and characterized by Fourier transform infrared and micro-Raman spectroscopy, powder X-ray diffraction and differential thermal and thermogravimetric analysis and nitrogen adsorption. The properties of the prepared salts are compared with those of the parent acid. Regarding the structural, textural and thermal and solubility characteristics, these salts are between salts of group A, with small metal ions, and B group salts with large metal ions. The acid salts are two phase mixtures of soluble acid and insoluble neutral salt, like other alkaline acid salts of H3PW12O40 for x < 2. The catalytic properties of the acid salts have been studied for the vapor-phase dehydration of ethanol, carried out in a conventional flow-type reactor at 300 °C. The acid salts exhibited stable catalytic activity, a little bit lower than tungstophosphoric acid for ethylene production from ethanol.

XRD powder patterns of AgxH3−xWPA and H3WPA (left: 24° < 2θ < 36°, right: 52° < 2θ < 64°).Figure optionsDownload as PowerPoint slide