| Summary: | Two types of amorphous ZrO<sub>2</sub> (am-ZrO<sub>2</sub>) catalysts were prepared by different co-precipitation/reflux digestion methods (with ethylenediamine and ammonia as the precipitant respectively). Then, copper and potassium were introduced for modifying ZrO<sub>2</sub> via an impregnation method to enhance the catalytic performance. The obtained catalysts were further characterized by means of Brunauer-Emmett-Teller surface areas (BET), X-ray diffraction (XRD), H<sub>2</sub>-temperature-programmed reduction (H<sub>2</sub>-TPR), and In situ diffuse reflectance infrared spectroscopy (in situ DRIFTS). CO hydrogenation experiments were performed in a fixed-bed reactor for isobutanol synthesis. Great differences were observed on the distribution of alcohols over the two types of ZrO<sub>2</sub> catalysts, which were promoted with the same content of Cu and K. The selectivity of isobutanol on K-CuZrO<sub>2</sub> (ammonia as precipitant, A-KCZ) was three times higher than that on K-CuZrO<sub>2</sub> (ethylenediamine as precipitant, E-KCZ). The characterization results indicated that the A-KCZ catalyst supplied more active hydroxyls (isolated hydroxyls) for anchoring and dispersing Cu. More importantly, it was found that bicarbonate species were formed, which were ascribed as important C<sub>1</sub> species for isobutanol formation on the A-KCZ catalyst surface. These C<sub>1</sub> intermediates had relatively stronger adsorption strength than those adsorbed on the E-KCZ catalyst, indicating that the bicarbonate species on the A-KCZ catalyst had a longer residence time for further carbon chain growth. Therefore, the selectivity of isobutanol was greatly enhanced. These findings would extend the horizontal of direct alcohols synthesis from syngas.
|
|---|
