[0017] The highly selective production of isobutylene from increased concentrations of ethanol in the feed stream is described in Examples 1B-1E. Notably, isobutylene yields of nearly 70% are obtained from the direct conversion of ethanol at molar concentrations in the feed stream exceeding 14%. And, as shown in Examples 1B- 1D, 1G, and 1I, the process of the present application also generates more of the higher-value co-products as compared to previously described processes. Specifically, valuable co-products such as propylene, phenol, meta-cresol and 3,5- xylenol are generated in higher quantities than seen with previously described ethanol to isobutylene conversion methods. Accordingly, the method described herein enables a process that generates isobutylene from high concentrations of ethanol and concomitantly results in the production of higher-value co-products.
[0018] Various aspects of the present application stems from the inventors’ unexpected finding that the highly selective conversion of ethanol to high purity isobutylene can be achieved at molar concentrations of ethanol in the feed stream equal to or exceeding 14% at steam to carbon (S/C) ratios of 0.05 to 3.0 utilizing a ZnxZryOz mixed oxide catalyst prepared by a co-precipitation method for the selective conversion of ethanol to isobutylene. Indeed, the inventors’ have observed isobutylene yields of nearly 70% of the maximum theoretical at ethanol feed concentrations exceeding those tested by Liu et al, and with isobutylene purities meeting or exceeding the requirements necessary for high purity isobutylene (>99.75%). In addition, levels of co-products (e.g., propylene, phenols, methane, etc.) relative to isobutylene are reduced relative to ZnxZryOz mixed oxide catalysts prepared via the hard template, impregnation, or inverse co-precipitation techniques.