High surface area tin oxide

Abstract

Abstract High surface area tin oxides are desirable catalyst carriers for emissions control including CO oxidation, VOC removal/methane combustion and NOx abatement. We have optimized literature procedures as well as developed proprietary recipes for the synthesis of porous SnO2 carriers. Precipitation of SnCl4 from homogeneous solution by urea and by hydrazine, the dissolution of Sn metal powder in HNO3, sol–gel routes from Sn alkoxides and inorganic Sn precursors, acid-induced gelation of K2SnO3, the Pechini method ex Sn(OAc)4 using various organic acids as dispersants and dry and wet thermal decomposition of Sn carboxylates have been investigated and compared. BET surface areas >100 m2/g have been achieved by a variety of methods after calcination in the temperature range 300–500 °C. High surface area tin oxides with excellent sintering resistance (250, 228, 190 and 175 m2/g after calcination at 300, 400, 500 and 600 °C, respectively) have been synthesized by the hydrazine method. Pt/SnO2 catalysts have been prepared by impregnation with Pt tetraamine hydroxide solution, and screened for propylene combustion and CO oxidation activity in a parallel 8 × 1 process optimization reactor. Light-off takes place at higher temperatures for CO oxidation than for propylene combustion due to Pt poisoning by CO at lower temperatures. High surface areas >200 m2/g could also be achieved by a modified Pechini method using aqueous glyoxylic acid as dispersant for Sn(IV) acetate. Ce–Sn–Co mixed oxides have been synthesized by the glyoxylic acid method, impregnated with Pt–Ru and found to be more active than Pt/Al2O3 for CO oxidation when using CO-only feed, but inferior to the Pt standard when feeding a CO–propylene mixture.