Linking Simultaneous In Situ WAXS/SAXS/Raman with Raman/ATR/UV–vis Spectroscopy: Comprehensive Insight into the Synthesis of Molybdate Catalyst Precursors

Abstract

A new setup is presented which enables simultaneous wide-and small-angle X-ray scattering (WAXS/SAXS) and Raman spectroscopic experiments during the synthesis of Mo-based mixed oxide catalyst precursors at the l-spot beamline at the Berliner Elektronenspeicherring-Gesellschaft für Synchrotronstrahlung (BESSY). Furthermore, we report about the separate monitoring of the same reactions under comparable conditions by simultaneous combined ATR/UV-vis/Raman spectroscopic measurements. For testing the performance of both experimental setups two syntheses were described comprising the precipitation of metal molybdates by mixing solutions of metal nitrates and ammonium heptamolybdate. Additionally, the effect of H 3 PO 4 admixture on precipitation was investigated. The combined evaluation of spectroscopic and WAXS/SAXS data allows the discrimination between different molybdate species appearing in solution and precipitate. Furthermore, these molybdate species could be assigned to separate phases of different crystallinity.

Nucleation and Crystal Growth of a {V14Sb8O42} Cluster from a {V15Sb6O42} Polyoxovanadate: In Situ XRD Studies

“…[1] In recent years the analytical tools for in situ investigations of chemical reactions under real reaction conditions were significantly developed. [2][3][4][5][6][7][8][9][10][11][12][13] We and others demonstrated that a wealth of information is gained by applying in situ XRD, in-situ total scattering, or in-situ X-ray absorption spectroscopy during chemical reactions. [10,[14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] Despite the increasing efforts to gain insight into mechanisms of chemical reactions, in situ X-ray scattering studies under real reaction conditions are still rarely performed.…”

Probing the Structural Changes and Redox Behavior of Mixed Molybdate Catalysts under Ammoxidation Conditions: An Operando Raman Spectroscopy Study

“…To probe the structural changes of catalysts under reaction conditions, in situ and, in particular, operando Raman spectroscopy are suitable tools . In the case of metal molybdates, it is possible to identify different molybdate structures by their characteristic spectroscopic features . Thus, we have demonstrated recently by operando Raman spectroscopy of mixed molybdate catalysts under propene oxidation conditions that the formation and changes of molybdate phases induced by exposure to different reaction gas mixtures can be followed by inspecting the intensity changes of their characteristic bands.…”

“…[6][7][8][9][10][11] In the case of metal molybdates,i t is possible to identify different molybdate structures by their characteristic spectroscopic features. [12][13][14][15][16][17][18][19] Thus,w ehave demonstrated recently by operando Raman spectroscopy of mixed molybdate catalysts under propene oxidation conditions [20] that the formation and changes of molybdate phases induced by exposure to different reactiong as mixtures can be followed by inspecting the intensity changes of their characteristic bands. In accordance with the above-mentioned in situ Mçssbauer experiments, [5] Inspiredb yt hese first optimistic results we extended our studies on the ammoxidation of propene to acrylonitrile over mixed molybdate catalysts ystems.…”

Surface and Bulk Approach to Time‐resolved Characterization of Heterogeneous Catalysts

“…Following these pioneering works, the liquid‐phase synthesis of these and other advanced materials has been subjected to scrutiny. In a short, and by no means an exhaustive survey, we can highlight more recent examples dealing with zeolites/zeotypes19, 20 and oxides 21. 22, 23 XRD–XAS–SAXS (SAXS:small angle X‐ray scattering) and Raman or, in some cases, UV‐visible spectroscopy combination(s), is (are) the preferred option(s), owing to inherent limitations of other techniques, which cannot easily handle signals evolving in the aqueous or organic media required by the synthesis.…”