Synthesis of Highly Ordered Hydrothermally Stable Mesoporous Niobia Catalysts by Atomic Layer Deposition

Abstract

A new class of mesoporous niobia catalysts has been synthesized by atomic layer deposition (ALD) of niobia within the pores of a mesoporous silica (SBA-15). Mesoporous materials after ALD cycles of niobia maintained the structural organization of SBA-15. Increasing loadings of niobia cause a decrease in the surface area, pore volume, and pore diameter due to the conformal coating of niobia within the pores. Materials containing 10, 19, and 30 cycles show remarkable hydrothermal stability, with minimal change in porosity and structural properties upon treatment in liquid water at 473 K. The mesoporous niobia material produced by 19 cycles has been studied as an acid catalyst for the gas-phase dehydration of 2-propanol, and for the dehydration of 2-butanol in both the gas and liquid phases, showing catalytic activity superior to commercial niobia (HY-340) per mass of material. Furthermore, deposition of Pd nanoparticles on this material consisting of SBA-15 coated with 19 cycles of niobia leads to a bifunctional catalyst for the transformation of γ-valerolactone to pentanoic acid, showing better stability versus time-on-stream compared to a conventional catalyst consisting of Pd supported on HY-340.