Lignin depolymerisation has received considerable attention recently due to the pressing need to find sustainable alternatives to fossil fuel feedstock to produce chemicals and fuels.
We report the role of the acidity of support during the selectivity hydrogenolysis of glycerol over supported bimetallic palladium–ruthenium (PdRu) catalysts. The PdRu nanoparticles were supported on a series of metal oxides and zeolitic supports via the modified impregnation method and tested for the liquid-phase hydrogenolysis of glycerol using gaseous hydrogen. The relative acid site densities of selected catalysts were determined by ammonia temperature-programmed desorption and pyridine desorption experiments. Based on these studies, we report a direct correlation between the catalytic activity (conversion and 1,2 propane diol yield) and two different acid sites (strong acid sites and very strong acid sites). Besides zeolite-supported catalysts, TiO
2
supported PdRu nanoparticles exhibit moderate catalytic activity; however, this catalyst shows high selectivity for the desired C–O bond cleavage to produce C3 products over the undesired C–C bond cleavage to produce < C3 products.
This article is part of a discussion meeting issue ‘Science to enable the circular economy’.
Controlling the selectivity of a reaction by rational designing of catalyst is an important and challenging topic in catalysis research. In this article, we report a strategy to tune the product selectivity during aqueous phase hydrogenolysis of glycerol using gaseous H 2. Ru/TiO 2 is an active catalyst for the hydrogenolysis of glycerol, however it promotes the hydrogenolysis of CÀ C bonds resulting in large quantities of C2 and C1 products. On the other hand, Pd/TiO 2 and Pt/TiO 2 catalysts are very selective for the hydrogenolysis of CÀ O bonds producing mainly C3 products (1,2 and 1,3 propanediols), however they are much less active compared to the Ru catalysts. In this article, we report that by combining Ru with Pt or Pd in a bimetallic nanoparticle, we can develop new catalysts that are both active and selective for CÀ O hydrogenolysis. A physical mixture of two monometallic catalysts does not show this enhanced selectivity for CÀ O hydrogenolysis, proving that intimate mixing of the two metals in a nanoparticle is crucial to tune the selectivity. All the monometallic and bimetallic catalysts have been characterised by microscopic and spectroscopic methods to understand their structural features. DFT studies were also done to rationalise the observed difference in the catalytic properties between monometallic and bimetallic catalysts.
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