Preparation Of Pd Based Catalyst Supported By Carbon Quantum Dots And Study On Hydrogen Production Of Formic Acid At Room Temperature

The international situation is changing rapidly,and the game between major countries is disturbing the transportation and utilization of fossil energy,especially oil and natural gas,and the fluctuating oil price is also stirring the hearts of the people.In the new energy strategy,hydrogen energy as an important energy source has become the focus of researchers’attention.Formic acid,as a kind of renewable and pollution-free material with low-cost and high hydrogen content,can be better integrated into the industrial production loop.It has become one of the representatives of hydrogen storage materials.However,the industrial application of formic acid dehydrogenation is restricted by the adverse reaction of toxic catalyst,harsh dehydrogenation conditions and the need of additives.Therefore,it is urgent to prepare a catalyst with high intrinsic activity,high cycle stability,high selectivity,no additives,and high efficiency of dehydrogenation at room temperature.In this paper,a series of supported heterogeneous formate dehydrogenation catalysts were designed and synthesized using citric acid monohydrate and ethylenediamine as raw materials to synthesize small molecule carbon quantum dots.It is mainly divided into two parts:（1）Carbon quantum dots with different nitrogen contents（CE-CD_S-I,CE-CD_S-II and CE-CD_S-Ⅲ）were prepared by hydrothermal method,and then CE-CD_S-X supported nanocatalyst of Pdwas successfully prepared by sodium borohydride reduction method.Represents Pd/CE-CD_S-I,Pd/CE-CD_S-II,and Pd/CE-CD_S-Ⅲ.The particle sizes of Pdmeasured in the experiment are about 2.65 nm,2.28 nm and 1.94 nm,indicating that the doping of nitrogen can effectively promote the dispersion of Pdparticles and limit the growth of Pdparticles.The TOF of Pd/CE-CD_S-Ⅲ reached 256h^-1 in the catalytic dehydrogenation of pure FA at 298 K at room temperature without additives,and the TOF of Pd/CE-CDS-Ⅲ reached 180 h^-1 after five cycles of dehydrogenation tests,showing good cyclic stability.It was found by gas chromatography that there was no dehydration side reaction in the process of hydrogen production by decomposition of formic acid,indicating that the prepared catalyst had100%selectivity for dehydrogenation reaction.The results show that the N-doped carbon quantum dots can not only avoid the growth of Pdparticles,but also improve the stability of the catalyst through the limiting effect.At the same time,the strong interaction between pyridine nitrogen and Pdmetal also plays an important role in the dehydrogenation reaction.（2）Using carbon quantum dot CE-CD_S-Ⅲ as the carrier（CE-CD_S is substituted in this chapter）and Pdas the main catalyst,the carbon quantum dot supported bimetallic catalyst is prepared by doping Au,Ru and Ag.By treating the carrier and adjusting the p H of the preparation environment,it was found that PdAg/CE-CD_S alloy catalyst formed PdAg alloy on the surface of carbon quantum dots with particle size of about 2nm.The results show that Pd_0.9Ag_0.1/CE-CD_S catalyst has the best catalytic effect on the catalytic performance of hydrogen production of carboxylic acid.At 298K,the TOF value can reach 619 h^-1,which is 2.41 times of Pd/CE-CD_S-ⅢTOF value.After five cycles,the activity retention rate reaches 73.3%.Moreover,the catalyst still maintained high catalytic activity after five cycles,and also maintained 100%H₂ selectivity.