Bismuth Molybdate Catalysts Prepared by Mild Hydrothermal Synthesis: Influence of pH on the Selective Oxidation of Propylene

Abstract

A series of bismuth molybdate catalysts with relatively high surface area was prepared via mild hydrothermal synthesis. Variation of the pH value and Bi/Mo ratio during the synthesis allowed tuning of the crystalline Bi-Mo oxide phases, as determined by X-ray diffraction (XRD) and Raman spectroscopy. The pH value during synthesis had a strong influence on the catalytic performance. Synthesis using a Bi/Mo ratio of 1/1 at pH ≥ 6 resulted in γ-Bi2MoO6, which exhibited a better catalytic performance than phase mixtures obtained at lower pH values. However, a significantly lower catalytic activity was observed at pH = 9 due to the low specific surface area. γ-Bi2MoO6 synthesized with Bi/Mo = 1/1 at pH = 6 and 7 exhibited relatively high surface areas and the best catalytic performance. All OPEN ACCESSCatalysts 2015, 5 1555 samples prepared with Bi/Mo = 1/1, except samples synthesized at pH = 1 and 9, showed better catalytic performance than samples synthesized with Bi/Mo = 2/3 at pH = 4 and 9 and γ-Bi2MoO6 synthesized by co-precipitation at pH = 7. At temperatures above 440 °C, the catalytic activity of the hydrothermally synthesized bismuth molybdates started to decrease due to sintering and loss of surface area. These results support that a combination of the required bismuth molybdate phase and a high specific surface area is crucial for a good performance in the selective oxidation of propylene.

Sol–Gel Synthesis of Bismuth Molybdate Catalysts for the Selective Oxidation of Propylene to Acrolein: Influence of pH Value and Theoretical Molar Atomic Ratio

“…Later, they were found to be capable of catalyzing the ammoxidation of propylene to acrylonitrile and the oxidation of propylene to acrolein . Their potential for further catalytic processes was extensively studied thereafter . Nowadays, they have became popular catalysts for the oxidation of light hydrocarbons .…”

Deposition of Visible Light Active Photocatalytic Bismuth Molybdate Thin Films by Reactive Magnetron Sputtering

“…Thus, in various studies bismuth molybdate photocatalysts were successfully used for the degradation of such dyes as methylene blue [13], rhodamine B [14,15,16], indigo carmine [17], the removal of antibiotics from the wastewater [8], and the decomposition of phenol [15]. Photocatalytic bismuth molybdates are typically synthesized using chemical methods, such as the hydrothermal method [8,18,19], molten salt method [20], solid state reaction [17] or the Pechini method [21]. However, to the best of our knowledge there are no commercial photocatalytic products based on the use of bismuth complex oxides available at the present time.…”

Formic Acid Modified Co3O4-CeO2 Catalysts for CO Oxidation

“…Meanwhile, with respect to synthesis strategy, hydrothermal synthesis is an efficient approach to prepare porous materials [9], while additives, such as urea, are helpful to synthesize well …”