Direct conversion of methane into oxygenates by H2O2 generated in situ from dihydrogen and dioxygen

Methane Oxidation to Methanol

The direct transformation of methane to methanol remains a significant challenge for operation at a larger scale. Central to this challenge is the low reactivity of methane at conditions that can facilitate product recovery. This review discusses the issue through examination of several promising routes to methanol and an evaluation of performance targets that are required to develop the process at scale. We explore the methods currently used, the emergence of active heterogeneous catalysts and their design and reaction mechanisms and provide a critical perspective on future operation. Initial experiments are discussed where identification of gas phase radical chemistry limited further development by this approach. Subsequently, a new class of catalytic materials based on natural systems such as iron or copper containing zeolites were explored at milder conditions. The key issues of these technologies are low methane conversion and often significant overoxidation of products. Despite this, interest remains high in this reaction and the wider appeal of an effective route to key products from C-H activation, particularly with the need to transition to net carbon zero with new routes from renewable methane sources is exciting.

Low temperature selective oxidation of methane to methanol using titania supported gold palladium copper catalysts

Selective oxidation of methane using AuPdCu/TiO₂ catalysts.

Poly[μ(4)-succinato-μ(2)-succinato-bis[diamminecopper(II)]]

In the title compound, [Cu(C₄H₄O₄)(NH₃)₂]_n, the Cu atom is coordinated by the N atoms of two ammonia mol­ecules and four O atoms from three different succinate ligands in a highly distorted octa­hedral geometry. The Cu atom and the C and O atoms of the succinate ligands lie on a mirror plane. Two adjacent CuO₄N₂ octa­hedra share one common O–O edge, forming a Cu₂O₆N₄ biocta­hedron with a Cu⋯Cu separation of 3.524 (2) Å. Neighboring biocta­hedra are connected by bis-unidentate succinate anions in the a-axis direction, while in the c-axis direction biocta­hedra are connected by bis-bidentate succinate anions, leading to an infinite two-dimensional network structure. These networks are further connected along the a-axis direction by hydrogen bonds between ammonia ligands and carboxyl­ate O atoms of neighboring network layers, forming a three-dimensional lamellar structure.

Synthesis, Structure and Magnetic properties of Chiral and Nonchiral Transition-Metal Malates

Carboxylate-bridged complexes of transition metals, M(II)=Mn(II), Fe(II), Co(II), Ni(II), Zn(II), were synthesised by reaction of M(II) salts with dl-malate and L-malate under hydrothermal conditions. These complexes form four series of compounds, which have been fully characterised structurally, thermally and magnetically. The crystal structures of the new chiral compounds, [Mn(L-mal)(H(2)O)] (1), [Fe(L-mal)(H(2)O)] (2), [Co(L-mal)(H(2)O)] (3) and [Zn(L-mal)(H(2)O)] (4) as well as those of the bimetallic analogues [Mn(0.63)Co(0.37)(L-mal)(H(2)O)] (5) and [Mn(0.79)Ni(0.21)(L-mal)(H(2)O)] (6) have been solved by single-crystal X-ray diffraction. The six L-malate monohydrates crystallise in the chiral space group P2(1)2(1)2(1) and consist in a three-dimensional network of metal(II) centres in octahedral sites formed by oxygen atoms. These structures were compared to those of the chiral trihydrate compounds [Co(L-mal)(H(2)O)]2 H(2)O (7), [Ni(L-mal)(H(2)O)]2 H(2)O (8) and [Co(0.52)Ni(0.48)(L-mal)(H(2)O)]2 H(2)O (9), which exhibit helical chains of M(II) centres, and those of dl-malate dihydrates [Co(dl-mal)(H(2)O)]H(2)O (10) and [Ni(dl-mal)(H(2)O)H(2)O (11) and trihydrate [Mn(L-mal)(H(2)O)]2 H(2)O (12) highlighting the great flexibility of the coordination by the malate ligand. UV/Vis spectroscopic results are consistent with octahedral coordination geometry of high-spin transition-metal centres. Extensive magnetic characterisation of each homologous series indicates rather weak coupling interaction between paramagnetic centres linked through carboxylate bridges. Curie-like paramagnetic, antiferromagnetic, ferromagnetic or weak ferromagnetic behaviour is observed and discussed on the basis of the structural features. The bimetallic compounds 5 and 6 represent new examples of chiral magnets.

A novel route for in-situ H2O2 generation from selective reduction of O2 by hydrazine using heterogeneous Pd catalyst in an aqueous medium

Hydrogen peroxide in high yields can be generated with high efficiency at mild conditions (25 degrees C and atmospheric pressure) with the formation of only environment-friendly by-products (N2 and H2O) by a reduction of O2 by hydrazine from its hydrate/salt with its complete conversion in a short reaction period (<or=0.5 h) using a easily separable supported Pd catalyst (Pd/Al2O3, Pd/Ga2O3 or Pd/C) in an acidic aqueous medium in the presence of bromide anions; the presence of both acid (protons) and bromide anions is essential for the selective reduction of O2 by hydrazine to H2O2 and in their absence, the reaction leads only to the formation of water.