Study On The PdCl₂-CuCl₂/AC Catalysts For The Synthesis Of Dimethyl Carbonate From Carbon Monoxide And Methyl Nitrite

Dimethyl carbonate?DMC? is an environmentally begin chemical, which can be widely used as fuel additive, green solvent, carbonylation or methylation agent and alternative to phosgene. The DMC synthesis from CO and methyl nitrite?MN? is a very economic synthetic reaction route. DMC is synthesized over the supported palladium catalysts and activated carbon?AC? supported Wacker-type catalysts showed the best catalytic performance. However, it is unclear that the influence of oxygenic functional groups of AC supported Wacker-type catalyst and potassium promoters of Wacker-type catalyst on the synthesis of DMC from CO and MN. In this paper, the influence of surface chemistry of AC and potassium promoters were investigated by combination of the reactivity with characterization results of catalysts prepared with nitric acid modified AC or potassium promoters.The reaction conditions of DMC synthesis from CO and MN were optimized as follows: gas hourly space velocity?GHSV? 4000 h-1, pressure 0.2 MPa, temperature 120 oC and CO/MN=1.0. Methanol and the coconut cell based activated carbon were used as solvent and support to prepare the optium AC supported Wacker-type catalyst.By modification of activated carbon with nitric acid, it is noted that the number of oxygenic functional groups?carboxylic, lactonic, phenolic groups? of AC had an important effect upon the synthesis of DMC from CO and MN. Combined the reactivity with Boehm titration, H₂-TPR and XPS characterization results, it is found that the phenolic group on AC contributed to the enrichment of Cu²⁺ on the catalyst surface and the easier reducibility of Cu²⁺, which further benefited the catalytic performance of DMC synthesis from CO and MN.The catalytic performance over PdCl₂-CuCl₂/AC catalysts with different potassium promoters ranked in the order: PdCl₂-CuCl₂-KCl/AC > PdCl₂-CuCl₂/AC > PdCl₂-CuCl₂-KOH/AC > PdCl₂-CuCl₂-CH3COOK/AC > PdCl₂-CuCl₂-K2CO3/AC. Especially, PdCl₂-CuCl₂-KCl/AC catalyst showed the best catalytic activities for DMC synthesis from CO and MN, and the STY of DMC was around 900 g.?L-cat?-1.h-1. H₂-TPR results demonstrated that the reduction temperature of Cu²⁺ for all catalysts ranked in the following order: PdCl₂-CuCl₂-KCl/AC < PdCl₂-CuCl₂-KOH/AC < PdCl₂-CuCl₂-CH3COOK/AC < PdCl₂-CuCl₂-K2CO3/AC, and XPS results proved that Cu²⁺/(Cu²⁺+Cu+) of PdCl₂-CuCl₂-KCl/AC catalyst was higher than that of PdCl₂-CuCl₂ /AC catalyst. So, the addition of KCl significantly promoted the reducibility of Cu²⁺, and contributed to the enrichment of Cu²⁺ on the catalyst surface, which led to the favorable DMC synthesis from CO and MN.