Recent Advances in Selective Propylene Oxidation over Bismuth Molybdate Based Catalysts: Synthetic, Spectroscopic, and Theoretical Approaches

Abstract

The selective oxidation of propylene to acrolein is an important reaction in the chemical industry which has been extensively studied over the last few decades. Today, spectroscopic, computational, and synthetic approaches allow a renewed view of this established and well-understood catalytic process at a fundamental level. Consequently, a revised mechanistic pathway for the selective propylene oxidation over bismuth molybdates has been suggested recently. Furthermore, studies concerning the local interaction of specific surface entities as well as concepts from semiconductor science have provided valuable information to describe the operation mode of oxidation catalysts. New synthetic methods can be used not only to tune the specific surface area and surface species of a catalyst but also to give direct access to distinct metal oxide phases or specific crystalline phases with a synergetic interplay on the nanoscale. Since complex multicomponent systems, which exhibit both higher selectivity and activity in comparison to pure bismuth molybdates, are used for industrial applications, it is important to transfer the research concepts from such model systems to those more complex systems. This also involves operando characterization techniques on multiple length scales. Recent research activities shine a renewed light on this well-studied reaction, which therefore may become one of the drivers in selective oxidation catalysis to apply and further establish new tools that have been developed in theory, modeling, synthesis, and operando spectroscopy.

Structural Evolution of Highly Active Multicomponent Catalysts for Selective Propylene Oxidation

“…Thus, the FSP-made Bi-Mo-Co-Fe oxide nanoparticles apparently underwent structural transformations on-stream in the early reaction stages due to their extreme activity. This is a typical behaviour for selective oxidation catalysts [4,5], resulting in poor conversion of propylene until a temperature of 320-330 • C was reached. After the initial structural transformation, both propylene conversion and exothermic behaviour of the catalysts were stable for the duration of testing (5-7 days).…”

“…The data presented in Figure 2a,b was recorded after these structural changes, whereby the FSP catalysts formed on-stream showed superior propylene conversion and product selectivity compared to the reference catalyst prepared by coprecipitation. The catalytic performance of the reference catalyst was poor since the applied oven temperature was rather low and dilution with SiC prevented hot-spot formation within the catalyst bed [5]. However, this was not the case for flame-made catalysts, which therefore exhibit highly potent material properties as selective oxidation catalysts at moderate temperatures.…”

“…Acrolein is a precursor for the synthesis of amino acids and an intermediate for the two-step oxidation towards acrylic acid, an important polymer building block [1,2]. Catalysts used for this process are typically multicomponent systems based on bismuth molybdate phases [3][4][5][6]. Recent studies have shown that such bismuth molybdates are accessible through a variety of novel synthesis methods [7][8][9][10][11][12], the choice of which can exert a strong influence on catalyst activity and performance [13].…”

“…In the case of complex nanostructured Bi-Mo-Fe-Co oxide catalysts prepared by FSP, a comprehensive multimodal and multiscale approach to characterisation is required [5]. Operando methodologies [23], along with advanced spectroscopic [24] and microscopic [25] analysis, offer a wide range of possibilities for understanding catalyst complexity.…”

Electrochemical synthesis of bismuth molybdates with controllable composition and their photocatalytic performance

“…Bismuth‐based semiconductor materials are widely recognized as visible‐light‐driven photocatalysts due to their good photochemical response to visible light . Among them, the bismuth molybdate family, including several phases in the Bi–Mo–O system, have been evaluated for environmental purification and remediation . Many researchers have examined and structurally characterized Bi 2 MoO 6 owing its unique layered structures and narrow band gap .…”