Catalytic dry reforming under industrially relevant conditions of high pressures and high temperatures poses severe challenges towards catalyst materials and process engineering. The demanding conditions under which the reaction is performed lead to a coupling of reactions occurring in the gas phase and reactions which are catalyzed by the material employed as catalyst. A profound analysis of the mechanisms occurring in gas phase and resulting products from gas phase reactions is key to understanding part of the challenges that any catalyst material, irrespective of its nature, will have to cope with. The deposition of coke on an active catalyst is as well one of the most limiting factors for catalyst lifetime and catalyst activity in dry reforming. Therefore, an understanding of the thermodynamics behind coke formation and an intricate description of the mechanisms driving the evolution of coke is a vital piece of the picture. Acid-base properties of the catalyst material and the role and nature of the active metal do also need to be considered. A large part of the review deals with mechanisms which are relevant for coke gasification and insights into materials properties, which are relevant to allow for reaction pathways along these lines. The review article focusses on research results which have been achieved using model systems -typically the analysis of model systems is a more rewarding exercise compared to fully formulated industrial catalyst systems, as here more elucidating structure-property relationships can be drawn. Additionally the article discusses dry methane reforming in the context of alternative syngas generation technologies and attempts to create an application perspective for the reader in the context of a sustainable approach towards carbon capture and storage.

Based on our newly developed microwave cavity perturbation technique, the microwave conductivity of diverse vanadium(III), (IV), and (V) phosphate catalysts was measured under reaction conditions for the selective oxidation of n‐butane. The conductivity response on the gas phase was identified as a very sensitive measure for the redox kinetics, reversibility, and stability of the samples, which are important prerequisites for highly selective and active catalysts. The sensitivity achieved by our method was comparable to surface‐sensitive methods such as X‐ray photoelectron spectroscopy, whereas more conventional analytic techniques such as X‐ray diffractometry or Raman spectroscopy only indicated the stability of the bulk crystal phase under the same reaction conditions.

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By quenching a melt of Li 4 P 2 O 7 two new, thermodynamically metastable polymorphs are obtained as biphasic mixtures. The crystal structure of one polymorph was determined from single-crystal X-ray diffraction data {Li 4 P 2 O 7 -trig*: colorless, trigonal, P3 2 12 (no. 153), Z = 3, a = 5.1699(2) Å, c = 18.9722(8) Å, 60 parameters, R 1 = 0.018, wR 2 = 0.051, 1265 unique reflections with F o > 4σ(F o )}. For the second polymorph a structure model was derived, using direct space methods followed by [a]

A holistic understanding of the key catalytic features of vanadyl­(IV) pyrophosphate enabling high maleic anhydride (MAN) yields in n-butane oxidation has fostered a debate which has continued since the finding of the catalyst. Under reaction conditions, vanadium­(V) orthophosphate structure fragments were detected on the surface of the catalyst. However, single-phase αII- and β-VVOPO4 reveal a much lower catalytic performance. This study shows that introducing Nb into αII-VOPO4 forming a solid solution (V1-x Nb x )OPO4 yields a bulk material with tunable catalytic properties. Selectivities of S MAN = 48% at a conversion of X n‑butane = 30% on (V0.1Nb0.9)­OPO4 are shown to be related to the isolation of surface V-sites, which surpass known VOPO4 catalysts by far. A boost in the overall n-butane consumption and MAN selectivity under alkane-rich feed conditions is shown to be another characteristic of (V1-x Nb x )­OPO4, leading to a highly increased MAN productivity. XPS studies reveal that a progressive replacement of V by Nb induces a reduction of the averaged oxidation state of near-surface V from +4.7 to +4.3, a finding that correlates linearly with an elevated MAN selectivity. This study experimentally confirms site isolation and electronic environment of the near-surface V-species as the key catalytic properties, from which catalyst design rules are derived to optimize partial oxidation reactions.

In the ternary system Eu/P/O the anhydrous phosphates EuII3(PO4)2, EuII3EuIII(PO4)3, EuIII3O3(PO4), EuIIIPO4, EuIII(PO3)3, and EuIIIP5O14 exist at equilibrium conditions (ϑ ≈ 1000 °C). A superstructure model for EuII3EuIII(PO4)3 [Eulytite structure family, Fdd2, Z = 24, a = 14.298(1) Å, b = 42.123(3) Å, c = 10.3887(9) Å] is proposed. The results of single‐crystal X‐ray diffraction (SXRD) studies on EuII10–xEuIIIx(PO4)6O1+x/2 (x ≈ 1.5), EuIII3O3(PO4) and ht‐EuIII(PO3)3 are reported. The crystal structures of the thermodynamically metastable phases EuIII2P4O13 (isotypic to YIII2P4O13) and lt‐EuIII(PO3)3 (isotypic to GdIII(PO3)3) were refined from X‐ray powder diffraction data (XRPD). According to our investigation for the oxide phosphide “EuII4OP2” an europium deficiency has to be assumed according to EuII4–xEuIII2x/3OP2 (x ≈ 1.5).

Ag 6 (V IV O) 2 (PO 4 ) 2 (P 2 O 7 ) was obtained by reaction of Ag 3 PO 4 and (VO) 2 P 2 O 7 (sealed ampoule, 550°C, 3 d). The crystal structure of the new mixed ortho-pyrophosphate was determined from X-ray single-crystal data [Pnma, Z = 4, a = 12.759(3) Å, b = 17.340(4) Å, c = 6.418(1) Å, R 1 = 0.071, wR 2 = 0.184 for 3174 unique reflections with F o Ͼ 4σ(F o ), 141 variables]. Ag + ions are located in between layers [(V IV O) 2 (PO 4 ) 2 (P 2 O 7 )] 6-. Equilibrium relations of the * Prof. Dr. R. Glaum E-Mail: rglaum@uni-bonn.de [a]424 new phosphate to neighboring phases were determined. The electronic structure of the (V IV ϵO) 2+ group was investigated by polarized electronic absorption spectroscopy (ν 1a = 9450 cm -1 , ν 1b = 9950 cm -1 , ν 2 = 14750 cm -1 ), EPR spectroscopy [X-and Q-band, powder and single crystal, orthorhombic crystal g-tensor with g 1 = 1.9445(3), g 2 = 1.9521(3), g 3 = 1.9695(3)], and magnetic measurements (powder, μ exp /μ B = 1.71, Θ p = -1.7 K).

Platinum group metal (PGM)-based catalysts are known to be highly active in the total combustion of lower hydrocarbons. However, through an alternative catalyst design reported in this paper by isolating PGM-based active sites in a tungsten phosphate matrix, we present a class of catalysts for selective oxidation of n-butane, propane, and propylene that do not contain Mo or V as redox-active elements. Two different catalyst concepts have been pursued. Concept A: isolating Ru-based active sites in a tungsten phosphate matrix coming upon as ReO 3 -type structure. Concept B: dilution of PGM-based active sites through the synthesis of X-ray amorphous Ru tungsten phosphates supported on SiO 2 . Using a high-throughput screening approach, model catalysts over a wide compositional range were evaluated for C3 and C4 partial oxidation. Bulk crystalline and supported XRD amorphous phases with similar Ru/W/P compositions showed comparable performance. Hence, for these materials, composition is more crucial than the degree of crystallinity. Further studies for optimization on second-generation supported systems revealed even better results. High selectivity for n-butane oxidation to maleic anhydride and propane oxidation to an acrolein/acrylic acid has been achieved.