A study of ZnxZryOz mixed oxides for direct conversion of ethanol to isobutene

•ZnxZryOz catalysts are selective for isobutene production from ethanol at high ethanol concentration.•Weak Brønsted acid sites are repsonsible for acetone to isobutene conversion.•Strong Brønsted acid sites are repsonsible for the coke formation and slow catalyst deactivation.•Activity of spent ZnxZryOz can be readily recovered by calcining in air. ZnxZryOz mixed oxides were studied for direct conversion of ethanol to isobutene. Reaction conditions (temperature, residence time, ethanol molar fraction, steam to carbon ratio), catalyst composition, and pretreatment conditions were investigated, aiming at high-yield production of isobutene under industrially relevant conditions. An isobutene yield of 79% was achieved with an ethanol molar fraction of 8.3% at 475°C on fresh Zn1Zr8O17 catalysts. Further durability and regeneration tests revealed that the catalyst exhibited very slow deactivation via coking formation with isobutene yield maintained above 75% for more than 10h time-on-stream. More importantly, the catalysts activity in terms of isobutene yield can be readily recovered after in situ calcination in air at 550°C for 2.5h. XRD, TPO, IR analysis of adsorbed pyridine (IR-Py), and nitrogen sorption have been used to characterize the surface physical/chemical properties to correlate the structure and performance of the catalysts.