Ketene Chemistry Research Articles

一酸化炭素の有効利用に役立つ遷移金属ケテン錯体の化学

Transition metal ketene complexes have drawn considerable attention as models for the possible intermediates implicated in the elementary carbon-carbon coupling step in surface-catalyzed or homogeneous carbon monoxide reduction. Although ketene chemistry has been investigated for over 80 years, there have been no review articles on chemistry of transition metal ketene complexes.Three separate aspects of transition metal ketene complexes are reviewed herein, 1) formation of ketene species on catalyst-surface, 2) the preparation and structures of transition metal ketene compexes, 3) chemical properties of transition metal ketene complexes.

The influence of substrate temperature on the surface chemistry of ketene on Pt(111)

Processes occurring during dosing of ketene on a heated Pt(111) surface were investigated using high-resolution electron energy loss spectroscopy and temperature-programmed desorption. During dosing at 400 K, CO and H 2 are evolved and ethylidyne accumulates on the surface. In contrast, at 350 K a C x H y species, not ethylidyne, is formed and some CO accumulates. It is postulated that small amounts of adsorbed carbon monoxide stabilize the C x H y species and inhibit ethylidyne formation.

Ketene: Ion chemistry and proton affinity

The gas phase ion-chemistry of ketene has been examined using a Quadrupole Ion Store (QUISTOR) as an ion-molecule reaction chamber. The ion chemistry of ketene is remarkably similar to that of the primary aliphatic alcohols and mercaptans and is characterized by associative and eliminative reactions of ions with a labile proton attached to the electronegative atom. The rate coefficients for the disappearance of CH 2 −+ and CO −+ in ketene were found to be 3.8 ± 1 × 10 −10 and 3.2 ± 0.5 × 10 −11 cm 3 molecule −1 s −1, respectively. The proton affinity of ketene as determined by the bracketing technique was estimated to lie between the proton affinities of dimethyl ether and 2-propanol at a value of 807 ± 8 kJ mol −1.

Positive ion probe of methane-oxygen combustion

The results of flame-ion mass spectrometry are used to probe the combustion chemistry of a premixed methane-oxygen flame of fuel-rich composition (equivalence ratio =2) burning at atmospheric pressure. Concentration profiles of a variety of positive ion species are obtained with good spatial resolution along the flame axis z. Neutral concentration profiles are available from molecular beam sampling studies of a similar flame. The individual positive ion profiles fall into characteristic, groups according to their chemistry in various ranges of the axial distance z in and near the reaction zone. Except for the very far upstream region, three ionic species (C2H3O+−C3H3+−H3O+) account for more than 85% of the total positive signal, and peak successively downstream along the z axis. The development of the major ion profiles is rationalized in terms of a scheme of ion-molecule reactions initiated by the formation of CHO+. The primary CHO+ continues downstream into a region dominated by formaldehyde and ketene chemistry, yielding CH3O+, C2H3O+ and C2HO+, as well as reaction with methane and its stripped products, methyl and methylene. In the higher temperature region just downstream of the reaction zone, the presence of considerable acetylene (∼10−2 mole fraction) determines the transition to C3H3+. Subsequently, the simpler products of combustion (O, H2O, CO) give rise to the ultimate H3O+ and secondary CHO+ with which it is in equilibrium. Further downstream (z>2 mm beyond the ‘end’ of the reaction zone), the behaviour of the ion chemistry is extraordinary in that small amounts of the species C+, CH+, CH2+ and CO+ persist in addition to H3O+ and CHO+; all six species maintain constant concentration ratios as they disappear by electron recombination. These observations provide evidence for the existence of amounts of the radicals C, CH and CH2 which greatly exceed their calculated equilibrium concentrations. The large amounts can be interpreted as arising from the decomposition and other reactions of acetylene produced in the reaction zone.

Texas group focuses on ketene chemistry

Texas group focuses on ketene chemistry