Boosting Butadiene Yield at Low Temperature from Ethanol Upgrading over the ZnO/LaPO ₄ Catalyst through HCO ₃ ^– Modification

The catalytic conversion of ethanol to butadiene contributes to reducing dependency on petroleum sources, along with the advantages of low cost and sustainability. A significant challenge involves the competition between dehydrogenation and dehydration at high temperatures (≥350 °C), which suppresses the C–C coupling process. To address this issue, we designed an HCO3– modified lanthanum phosphate support that shows an improved surface area and reduced surface acidity. After loading zinc oxide, the obtained ZnO/LaPO4 catalyst efficiently converts ethanol to butadiene, showing a yield of 33.2% with a weight hourly space velocity of 0.73 h–1 at 300 °C. The improved surface area of the catalyst is beneficial for ethanol adsorption and diffusion, while the reduced surface acidity suppresses the ethanol dehydration reaction. The highly dispersed dehydrogenation sites, [Zn–O–P], formed via phosphate coordination anchoring zinc oxide, result in efficient low-temperature ethanol activation. Kinetics experiments and in situ diffuse reflectance infrared Fourier transform spectroscopy indicate that the pathway follows ethanol dehydrogenation to acetaldehyde over the [Zn–O–P] sites, while the surface-exposed La3+ sites facilitate acetaldehyde coupling and dehydration to yield butadiene. The synergy between [Zn–O–P] and La3+ steers the reaction pathway toward carbon-chain growth, in turn suppressing the competitive direct dehydration of ethanol to ethylene/ether. Furthermore, the catalyst exhibits excellent reusability. This study provides a strategy for converting ethanol to butadiene at low temperatures.