Support and dispersion effects on activity of platinum catalysts during wet oxidation of organic wastes

Abstract

Catalytic activity of platinum catalysts such as Pt/graphite, Pt/TiO 2 , Pt/Al 2 O 3 , and Pt/active carbon was studied using a slurry phase CSTR. Three model reactions, namely, phenol, maleic acid, and malonic acid oxidation were investigated in the temperature range from 120 to 170°C and at a total reactor pressure of 1.7 MPa. Platinum on graphite was found to be most suitable for aqueous phase oxidation of phenol, maleic acid, and malonic acid. Complete conversion for both phenol oxidation as well as maleic acid oxidation to CO 2 was observed with Pt/graphite at stoichiometric oxygen excess close to 0% and at 150°C. Deactivation due to over-oxidation is gradual for Pt/graphite with a metal dispersion of 5.3% as compared to Pt/TiO 2 , Pt/Al 2 O 3 and Pt/AC, which have metal dispersions of 15.3%, 19.5% and 19.0%, respectively. It was further found that in the presence of Pt/graphite catalyst and oxygen, malonic acid reaction proceeds via non-catalysed decarboxylation, and catalytic decarboxylation to CO 2 and acetic acid, and catalytic oxidation to CO 2 and H 2 O. Acetic acid was found to be difficult to oxidise at temperatures below 200°C. KEY WORDS: platinum catalysts; catalytic supports; wastewater treatment; stoichiometric oxygen excess; platinum metal dispersion Nomenclature AC active carbon concentration of the compound i [mol/m 3 ] CWO catalytic wet oxidation molar flow rate of compound i [mol/s] volumetric flow rate [m 3 /s] F L V volumetric flow rate of liquid [m 3 /s] n c number of carbon atoms in a compound [-] P pressure [Pa] Pt platinum R w;i specific disappearance rate of compound i [mol/s.kg] SCWO supercritical water oxidation S !i selectivity to compound i [%] S.E. stoichiometric oxygen excess to model compound [%] T temperature [K] V L volume of the liquid in the reactor [m 3 ] W total mass of dry catalyst in the reactor [kg] WAO wet air oxidation conversion of compound i [%]

Pathways for biomass‐derived lignin to hydrocarbon fuels

“…42,43 Among these, TMPL process requires little or no chemical and converts wood-chips to fi ber for papermaking by mechanical friction and compression, likely resulting in minimal chemical and structural alteration to the lignin matrix. By comparison with native lignin, TMPL lignin does not retain the primary structure decrease the degree of polymerization and/or the oxygen content of biomass have involved various transformations, including hydrothermal decarboxylation, 47 acidcatalyzed dehydration, 48 hydrogenolysis, metal-catalyzed decarboxylation, 49 pyrolysis, 50 carbonization, 51 and metalcatalyzed hydrogenation. 52 Selective hydrogenolysis of lignin could increase hydrogen content and decrease oxygen content while lowering molecular weight by reductive cleavage of C-O-C bonds, producing potential fuel precursors or other value added chemicals.…”

Catalytic wet air oxidation of phenol over CeO2-TiO2 catalyst in the batch reactor and the packed-bed reactor

“…Transition metal oxides catalysts showed good activity, while leaching metal ions from the solid catalysts could lead to the deactivation of the catalysts [13][14][15][16]. Noble metal catalysts with the high cost were studied, and showed excellent activity and stability [17][18][19][20].…”

Catalytic wet oxidation of organic compounds over N-doped carbon nanotubes in batch and continuous operation

“…It is important to note that the formation of carbonaceous deposits on the surface of the catalyst and the over-oxidation of Pt were not evaluated. However, these phenomena are known to originate the deactivation of Ptbased catalysts in CWO [15,16,49]. Taking into account the high Pt demands and costs, Ptfree CNT-BM-M is a better alternative for waste water treatment by CWO, achieving high phenol removal in addition to the fact that it can be prepared by a cost effective and easy to handle method, avoiding the use of solvents and production of wastes.…”