Investigation On Preparation Of Environment-friendly Nano-noble Metal Catalyst Supported On Porous Matrix And Their Catalytic Hydrogenation Properties

Supported noble metal nanoparticles(NPs) catalysts have attracted sustained attention in the field of catalysis and being widely applied in various catalytic reaction, such as hydrogenation, reduction, oxidation and reforming because of their advantages of easy separation operation and good reusability. However, the traditional preparation methods of supported noble metal NPs catalyst always use organic precious metal precursor which was toxic and harmful to the body and organic solvents as raw materials. The prepared catalysts were difficult to simultaneously satisfy the catalytic activity, selectivity and reusability in reactions, causing the increase of environmental load and pollution. Therefore, it has been a vital significance and value to prepare environment-friendly supported noble metal catalysts with excellent catalytic properties.Bayberry tannin(BT) was a kind of natural plant polyphenolic compound with a stable molecule and higher reactivity characteristics. BT was used as a suitable material to prepare novel supported catalyst with excellent catalytic performance in activity, selectivity and reusability. Because BT can realize surface modification of porous materials(such as Si O2, Al2O3) and the modified materials could be used as an excellent matrix to support noble metal NPs, achieving a high dispersion and effective imm obilization of the NPs. In the present study, we have prepared three kinds of supported catalysts including Pd/Si O2-BT, Pt/Si O2-C and Pt/Al2O3-C by using the porous materials of Si O2 and Al2O3 that modified by BT as matrix to support the Pd and Pt NPs. Their physical and chemical properties were characterized by ICP-OES、TG、FT-IR、TEM、XRD、XPS、BET and EA method. Subsequently, the unsaturated olefin(such as propylene alcohol and cinnamaldehyde) were utilized as the catalytic substrates to investigate the catalytic properties. The experimental results were concluded as follows:In the first part, a novel heterogeneous Pd/Si O2-BT catalyst was prepared by loading Pd2+ on BT modified Si O2, followed by reduction of Na BH4. EA analysis showed that-NH2 was successfully grafted onto the Si O2. SEM and TEM analysis suggested that Pd NPs were highly dispersed in Si O2, the average diameter were in the range of 1.68±0.40 nm when the ratio of BT and Si O2 was 10:1. The catalytic activity and reusability of Pd/Si O2-BT catalyst(the ratio of BT and Si O2 was 10:1) was evaluated in hydrogenations of allyl alcohol, benzaldehyde and cinnamaldehyde, which prepared with Pd/Si O2 and commercial Pd/C catalyst. It was shown that the conversion of Pd/Si O2-BT catalyst in allyl alcohol hydrogenation reaction could reach 85.64% in 30 min. The catalytic activity decreases only 15.17% after 5 cycles, exhibiting excellent reusability. At the same time, the hydrogenation reaction of the catalyst in the benzaldehyde and cinnamaldehyde also exhibited a higher catalytic activity.In the second part, we prepared a novel Pt/Si O2-C catalyst which by loading Pt4+ on modified Si O2 with BT, followed with reduction of Na BH4 and carbonization. The experimental results showed that Pt NPs obtained by 500℃carbonization process were highly dispersed in Si O2, which average diameter were in the range of 12.57±2.30 nm. The catalytic properties of Pt/Si O2-C catalyst was investigated by using liquid hydrogenation of cinnamaldehyde as model reaction. The result showed that the highest activity and good reusability was obtained when the Si O2/BT was 10:1, the concentration of Na BH4 was 0.2M, the reduction temperature was 25℃ and the carbonization temperature was 500℃. The conversion rate of cinnamaldehyde reached 82.98% in 6h, the selectivity of COL was 91.33% and after 5 cycles, the activity was about 81.18% of that in the first run.In the third part, the Pt/Al2O3-C catalyst was prepared by loading Pt4+ on modified Al2O3 with BT, followed with reduction of Na BH4 and carbonization. The characterization results showed that the Pt nanoparticle which carbonized at 800℃ mainly in the form of metal well dispersed at Si O2 surface with average diameter of 6.34±0.40 nm. The catalytic properties of Pt/Al2O3-C catalyst was investigated by using liquid hydrogenation of cinnamaldehyde as model reaction with KOH-ethanol as solvent. The result showed that the highest activity, selectivity and good reusability was obtained when the Al2O3/BT was 10:1, the concentration of KOH was 0.037 M and the carbonization temperature was 800℃. The conversion rate of cinnamaldehyde reached 97.76% in 30 min, the selectivity of COL was 88.30% and after 4 cycles, the activity was about 89.70% of that in the first run, exhibiting excellent reusability.