Sn and Zn modified HZSM-5 for one-step catalytic upgrading of glycerol to value-added aromatics: Synergistic combination of impregnated Sn particles, ALD introduced ZnO film and HZSM-5 zeolite

- Introduction of Zn species improved conversion efficiency of carbon in glycerol.
- Sn/HZSM-5 modified by ZnO film of 20 ALD cycles lead to better synergistic effect.
- Sn particles on HZSM-5 would be completely packaged by ZnO film of 40 ALD cycles.
- The catalyst reusability could be tremendously improved by ALD introduced ZnO film.

The chemoselective catalytic conversion of glycerol into high value-added aromatics (GTA) can greatly enhance the economic profits in biodiesel and biomass industry chain. In order to enhance the aromatization activity, stability and conversion efficiency of carbon in glycerol into aromatics during the GTA process, Zn species, which could directly convert alkenes originated from deoxygenation of glycerol into aromatics through dehydrogenation reaction, was introduced into Sn/HZSM-5 zeolite via atomic layer deposition (ALD) and incipient wet impregnation (IWI) method. Compared with impregnated ZnO modified Sn/HZSM-5, ZnO introduced by 20 ALD cycles into Sn/HZSM-5 deposited in the form of thin film, which not only fully coated both HZSM-5 external and internal surface, but also partially covered impregnated Sn particles. This film stabilized the oxidation state of loaded SnOx species which acted as catalytically active materials and further healed HZSM-5 structural defects, leading to the better synergistic effect among HZSM-5 zeolite, impregnated Sn particles and ALD introduced ZnO films. Besides, the reusability of this catalyst could be tremendously improved due to the protective effect of introduced ALD ZnO film which could prevent irreversible dealumination of HZSM-5 from exposure of HZSM-5 framework to steam during GTA reaction and regeneration procedure. However, when the deposited ZnO ALD cycle number reached 40, Sn particles on HZSM-5 could be completely packaged by ZnO film, on which occasion Sn could not participate in the GTA process, thereby leading to the reduction in both aromatics yields and catalyst lifetime.

205Modification of a Sn/HZSM-5 catalyst by thin 20 ALD cycle deposited ZnO films lead to better synergistic aromatization effect.