Study Of The Palladium-Based-Catalysts For Methanol Synthesis

Methanol is a widely used and globally distributed product with number of industrial applications.In chemical industry,commercial uses of methanol include the production of formaldehyde,aromatics,ethylene,methyl tertiary butyl ether?MTBE?,acetic acid and other chemicals.It is also very important due to the current depletion of fossil fuel resources.It is considered to be an ideal alternative fuel due to fast dismissing oil and gas resources.There is also a growing demand for methanol in fuel application such as production of dimethyl carbonate?DMC?,biodiesel production,the direct blending into gasoline and it could provide conventional energy storage for fuel cell applications.The energy resources structure of "rich in coal,poor in petroleum less gas” decided the commercial production of methanol is mainly from coal-based syngas in our country,coal-based syngas generally contains at least 40 ppm sulfur,while conventional Cu/ZnO/Al2O3 catalysts for methanol synthesis do not tolerate more than 0.1 ppm H₂ S due to the formation of metal sulfides.Pd-based catalysts are considered a promising sulfur-tolerant catalysts.The research of Pd-based catalysts mainly divided into the carrier,promoter and the catalytic mechanism.In this paper three works have been done:?1?Monoclinic ZrO₂ and tetragonal ZrO₂ were used as supports to prepare Pd/ZrO₂ catalysts.The effect of zirconia phase on the activity of Pd/ZrO₂ for the methanol synthesis was investigated.For a fixed Pd loading,Pd/m-ZrO₂ was three times more active for methanol than Pd/t-ZrO₂ under the same conditions.Increasing the Pd loading on m-ZrO₂ resulted in further improvement in CO conversion with minimal change in CH3 OH selectivity.The catalysts were then characterized using H₂-TPR,CO-TPD and XPS.Results demonstrated that Pd/m-ZrO₂ have lower reduction temperatures,stronger adsorption capacity of CO and more oxygen defects are conducive to the formation of intermediate products,so as to improve the activity.?2?Ce and La modified m-ZrO₂ were prepared as carriers for Pd-based catalysts.The activity of Pd/Ce-mZrO₂ and Pd/La-mZrO₂ for the methanol synthesis was investigated.The results showed that conversion of CO over Pd/Ce-mZrO₂ and Pd/La-mZrO₂ catalysts were lower than Pd/m-ZrO₂,XPS characterized showed oxygen defects reduced was the main reason.But methanol selectivity over Pd/Ce-mZrO₂ and Pd/La-mZrO₂ catalysts were higher than Pd/m-ZrO₂ due to the chemical bonding such as Pd–O–Ce and Pd–O–La??3?Mesoporous Ce_xZr_1-xO₂ solid solutions were prepared by the surfactant-assisted method with Hexadecyl trimethyl ammonium Bromide?CTAB?as templats ?Ce?NO₃?₃·6H₂O as cerium resource and Zr?NO₃?₃·5H₂O as zirconium resource.The diffraction patterns of Ce_xZr_1-xO₂ are similar to the cubic fluorite structure of CeO₂.N2 adsorption analysis showed that the Ce_xZr_1-xO₂ were wormhole-like mesostructures and hierarchical scaffold-like mesoporous structures.Pd/Ce_0.8Zr_0.2O₂ exhibited highest CO conversion and methanol selectivity.