Linear CO Research Articles

Carbon-13 magic angle spinning NMR study of carbon monoxide adsorption on ruthenium-exchanged zeolite Y

Three types of adsorbed carbon monoxide are observed on Ru-Y zeolite by /sup 13/C magic angle spinning NMR: linear, bridged, and dicarbonyl CO. Samples exposed to CO at room temperature exhibit only linear and dicarbonyl species. At higher adsorption temperature bridged species are formed and a relative increase in dicarbonyl adsorption is observed. A smaller percentage of linear species is produced at high temperature. The electronic environments of linearly bonded CO are more diverse than those of bridging and dicarbonyl moieties. CO/sub 2/ is formed over Ru-Y zeolite upon initial exposure of the catalyst to CO at room temperature, apparently through reaction with unreduced metal oxide. 20 references, 2 figures, 1 table.

An infrared spectroscopic study of CO on Cu(111): The linear, bridging and physisorbed species

The chemisorption of CO on Cu(111) in the temperature range 7–77 K has been investigated with infrared reflection absorption spectroscopy and LEED. Initial adsorption at 7 and 77 K is characterised by the appearance of a linear CO species ( ν( CO) = 2078−2070 cm −1). Adsorption to higher coverages at 77 K, when the CO overlayer produces a hexagonal LEED pattern, gives rise to additional infrared bands at frequencies associated with bridging species (ν(CO) = 1830 and 1812 cm −). The same overlayer of CO at 7 K exhibits only one of the two bridging CO bands ( ν ( CO) = 1830 cm −1) as well as the linear band. The temperature dependence of the bands in the bridging region is explained in the same way as similar observations for CO adsorption on Pt(111). Experiments at these low temperatures have also enabled us to study physisorbed CO ( ν( CO) = 2141−2138 cm −1) with infrared spectroscopy. Even at 7 K the physisorbed species does not adsorb on the bare surface: almost saturation coverage of the chemisorbed species is required.

Normal Unenhanced Raman Spectra of CO and CH4Adsorbed on Cobalt(poly)

Abstract Normal unenhanced Raman spectra (NURS) of low-polarizability CO molecules were observed for the first time on cobalt at R. T. and residual gas pressure. We assign five bands observed between 2030–2130 cm−1 to linear chemisorbed CO species, while those observed between 1840–2010 cm−1 have been ascribed to the 2-fold chemisorbed species. The three bands observed between 1740–1830 cm−1 we believe are due to the 3-fold species. The corresponding fourteen Co-C stretches were observed and assigned. A model based upon electron backdonation is proposed for each of the three structures. NURS were also observed at R. T. for physisorbed CH4 and assignments are made to the four frequencies of CH4.

An infrared study of the oxidation of carbon monoxide over supported rhodium catalysts

The reaction of carbon monoxide and oxygen over supported rhodium films has been studied using infrared spectroscopy. The focus of the work was the reactivity of the various CO/Rh/X (X = Al 2O 3, SiO 2, TiO 2) surface states for supported catalysts having high and low Rh loading. Under the reaction conditions the “linear CO” species was the most stable toward oxidation, but this could have been a result of an oxidized Rh surface. A new CO/Rh surface species has been proposed which exhibits an infrared band at 2000 cm −1 for a 0.5% Rh/TiO 2 film. This species is believed to be a bridged carbonyl between Rh 1+ and the TiO 2 support.

Normal unenhanced Raman spectra of CO and residual gas adsorbed on Ni(111)

Normal unenhanced Raman spectra (NURS) of low-polarizability molecules adsorbed on Ni(111) at 98 K. have been recorded at residual gas pressure. This is the first observation of Raman spectra from low-polarizability molecules adsorbed at low pressure onto a poor Raman signal enhancer. Raman bands were also recorded from Ni(111) at 98 and 298 K after exposing the crystal to 10 6 L CO. Assignments of CO stretches and their corresponding Ni-C stretches are discussed for both linear and bridge CO adsorbed with different neighboring species. Two low-lying vibrational modes of CO were recorded at 80 and 185 cm −1 and assigned to the CNiNi bend (on-top) and the OCNi bend (bridged), respectively. Other Raman bands are assigned to vibrations of oxygen, ozone, and hydrogen adsorbed on Ni(111).

Adsorption of carbon monoxide on a smooth palladium electrode: an in-situ infrared spectroscopic study

Adsorption of carbon monoxide on a smooth palladium electrode in 1 M HClO/sub 4/ saturated with CO was studied by two in-situ IR reflectance spectroscopic methods: EMIRS (electrochemically modulated infrared reflectance spectroscopy) and LPSIRS (linear potential sweep infrared reflectance spectroscopy). Two types of adsorbed CO, linear and bridged, were identified from the observed IR spectra, the latter being the predominant surface species. The C-O stretching frequency of the linear CO shifts to higher frequencies at more positive potentials with a slope of 48 cm/sup -1//V. The frequency of the bridged CO increases by 63 cm/sup -1/ between -0.5 and 0.9 V(NHE) and its integrated band intensity decreases continuously in the same potential region while the intensity of the linear CO is almost constant up to 0.1 V and then decreases gradually with increasing positive potential. The surface selection rule of the IR reflection absorption spectroscopy was tested for the present system by using the p- and s-polarized light. It was found that only p-polarized light gave the IR spectra of CO adsorbed on the palladium electrode thus proving the selection rule at the electrode/solution interface.

ChemInform Abstract: EFFECTS OF PREPARATION PROCEDURE ON THE SURFACE PROPERTIES OF RHODIUM SUPPORTED ON Γ-ALUMINA

The decomposition of rhodium(III) nitrate, chloropentamminerhodium(III) chloride and rhodium(III) sulphite in atmospheres of hydrogen, nitrogen and nitrogen (80%)+ oxygen (20%) have been investigated by thermogravimetric analysis with the salts either pure or impregnated onto a γ-alumina support. The decomposition of rhodium(III) sulphite failed to give dispersions of rhodium metal on alumina but the reduction of the other salts to Rh0 was complete in nitrogen or hydrogen at temperatures between 400 and 690 K.Hydrogen and CO uptake data have shown that rhodium(III) nitrate led to a more finely divided dispersion of metal than did chloropentamminerhodium(III) chloride. Infrared spectra of CO absorbed on the Rh/Al2O3 dispersions were consistent with this conclusion. The effects of sintering and oxygen adsorption on the infrared spectra are reported. Linear and bridge-bonded CO were formed on exposed metal planes or two-dimensional rafts at Rh0 sites which were also active for the chemisorption of oxygen. Gem-dicarbonyl species were formed at monatomically dispersed rhodium sites or edge sites in rafts, both of which had cationic character through interaction with the alumina support. These sites were not active for the adsorption of oxygen.

Conformational energetics in hydrogen-bonded dimers. The unobserved COHF complex

Ab initio electronic-structure calculations with large basis sets and extensive treatment of electron correlation have been carried out for the COHF complex. The potential surface exhibits a local minimum for linear COHF that is over 400 cm −1 above the absolute minimum that corresponds to the OCHF structure. The main reason for the difference in the stabilities of the two conformers is the difference in their electron-correlation energies. The interconversion of COHF to OCHF follows a minimum-energy path that takes the complex through a structure where the fluorine end of HF points into the middle regions of CO.

Surface reaction rate of hydrogenation of adsorbed carbon monoxide as examined by an emissionless infrared diffuse reflectance spectrometer

The behaviors of adsorbed CO species during the methanation of CO on supported metal catalysts were examined by using an EDR (emissionless infrared diffuse reflectance spectrometer). Major adsorbed species observed under steady-state CO-H/sub 2/ reaction were adsorbed CO and surface formate, and appreciable absorption could not be observed in C-H and O-H regions. The rate constants of disappearance of adsorbed species on 0.5% Pd/Al/sub 2/O/sub 3/ under the reaction conditions were also measured from the transient responses of IR spectra. The intensities of the bands due to surface formate did not change with time, showing that the surface formate is not an intermediate. The rate constants of disappearance of adsorbed CO (linear CO and bridge CO) were essentially identical with each other and were in good agreement with the rate constant of CH/sub 4/ formation measured by PSRA (pulse surface reaction rate analysis). These data indicate that the rate-determining step in the methanation of CO is the C-O bond dissociation of adsorbed species and the hydrogenation of the adsorbed carbon species proceeds rapidly. 8 figures, 1 table.

Infrared study of trapped carbon dioxide in thermally treated apatites

The formation of molecular CO 2 in synthetic apatites (prepared in aqueous systems), dental enamel, dentine, and various apatitic rock phosphates after heating in the range 120–900°C has been investigated by infrared spectroscopy. The CO 2 band at 2340 cm −1 was observed in the synthetic samples, enamel, and some of the rock phosphates, but not in dentine or bone. It is suggested that the absence of this band in dentine and bone is caused by the small crystal size of their apatites. The CO 2 band at 667 cm −1 was never observed. The polarized infrared spectrum of heated dental enamel showed that the linear CO 2 molecules were either randomly oriented or oriented so that the length of the molecules made an angle of about 56° with the c axis. It is suggested that, if the latter is correct, the CO 2 originates from a CO 2− 3 ion which occupied the sloping face of the phosphate ion site.

Infrared studies of CO adsorption on reduced and oxidized [formula omitted

Carbon monoxide adsorption experiments were studied on reduced and oxidized Pt TiO 2 with FT-IR. On reduced samples two kinds of linear CO species were observed and assigned as adsorption on Pt close-packed (terrace) sites (2094 cm −1) and on Pt open (step) sites (2077 cm −1). In addition a bridged CO species was found at 1854 cm −1. Both linear species show increasing frequencies with coverage. Saturation CO uptake decreases with increasing substrate reduction temperature and there is a preferential decrease of linear CO species on terrace sites and the concentration of bridged species lies below detection limits. On oxidized Pt TiO 2 samples, some Pt atoms are covered with oxygen atoms and the density of step sites is enhanced. On these surfaces there are two kinds of linear CO species assigned to terraces (2130 cm −1) and steps (2101 cm −1) and a bridged CO species at 1880 cm −1. In addition, several CO species are found which are also detected on reduced samples. These species show intensity variations during lengthy exposures. Preadsorbed linear CO species (2130, 2094, and 2077 cm −1 bands) on oxidized samples are also sensitive to H 2 exposures.

Atomic structures of oxymyoglobin and oxyhaemoglobin and the cooperative mechanism of oxygen binding

Until very recently, it had not been possible to determine the structures of oxymyoglobin and oxyhaemoglobin, because the crystals autoxidized. My colleagues S. E. V. Phillips and B. Shaanan have been able to overcome this problem. Phillips did an X-ray analysis of sperm whale oxymyoglobin at 1.6 Å resolution, followed by a neutron diffraction analysis at 1.7 Å resolution in collaboration with B. Schoenborn. Shaanan solved the structure of human oxyhaemoglobin at 2.1 Å resolution. These analyses have provided firm stereochemical data about the conformation of the haem and the geometry of the FeO 2, bond. They have also revealed the role of the distal histidine in discriminating between O 2 and CO. Bent geometry for the FeO 2 bond with an FeOO angle of 114° was predicted by Pauling. This prediction was confirmed by X-ray studies of J.P. Collman's oxygenated picket fence complexes, except that the FeOO angle there was 130°. Intuitively, one would have expected that angle to be determined by the nature of the FeO 2 bond, and to remain the same in all oxygenated haem derivatives, but this is not true. The FeOO angle is 115(±5)° in oxymyoglobin and 156(±10)° in the α and β oxyhaemoglobin. The difference is due to the different constraints imposed by the distal residues in the haem pocket (His E7, Val E11 and Phe CD1). Collman's picket fence complexed with dimethylimidazole has a partition coefficient between O 2 and CO of 4280; the same complex with a covalently attached imidazole has a partition coefficient of 26,600. By contrast, the partition coefficients of myoglobin and haemoglobin are 150 and 250 respectively. If they were as high as in the picket fence complex, respiratory transport by haem proteins would not be possible, since CO is produced endogenously in the breakdown of porphyrin (one mol CO per mol porphyrin). How do the two proteins discriminate between O 2 and CO? The electronic structures of the two ligands ensure that O 2 binds preferentially in the bent conformation, while CO prefers to bind linearly with FeCO on the haem axis. The distal pockets in the myoglobin and haemoglobin are tailored so as to fit the bent oxygen, but to oppose the binding of the linear CO which is forced off the haem axis by steric hindrance. This appears to be one of the discriminating devices. The other consists of hydrogen bonding by the distal histidine. Solvent effects and spectroscopic evidence suggested that the FeO 2 bond is polar, with transfer of negative charge from the iron to the oxygen, while the FeCO bond is purely covalent. Pauling first suggested that the distal histidine could form a hydrogen bond to the terminal oxygen which carries a formal negative charge in his view of the FeO 2 complex. Evidence suggesting such a bond comes from electron paramagnetic resonance and oxygen affinity data on cobalt-substituted haemoglobins and myoglobins. Phillips and Schoenborn have now proved the existence of that hydrogen bond by a neutron diffraction analysis of oxymyoglobin. In D 2O at pH 8.4 the distal histidine carries one exchangeable deuteron which can bind either to N ϵ facing the bound haem ligand or to N δ, facing the external solvent. The neutron maps showed that in oxymyoglobin the deuteron is on N ϵ forming a hydrogen bond with the bound oxygen, while in carbonmonoxymyoglobin it is on N δ, facing the solvent, and the histidine is further removed from the ligand. This result confirms the polar character of the FeO 2 bond and the non-polar character of the FeCO bond. It also tells us that nature employs not one but two methods to discriminate between the two ligands. Eisenberger et al. used extended X-ray absorption fine structure (EXAFS) to measure the FeN distance in deoxyhaemoglobin and concluded that the irons lie only 0.2 +0.1 −0.2 Å from plane of the porphyrin nitrogens and that the cooperative mechanism I had proposed is therefore invalid. We have now compared the EXAFS of deoxyhaemoglobin with that of the ferrous ‘picket fence’ 2-methylimidazole complex in which the displacement of the iron from the plane of the porphyrin nitrogens is known to be 0.399 ± 0.004 and 0.426 ± 0.004 Å from the mean porphyrin plane. The two EXAFS spectra are very similar, consistent with similar displacements of the irons. We find the same FeN distance of 2.06 ± 0.01 Å in deoxyhaemoglobin as Eisenberger et al., but show that the displacement of the iron cannot be calculated from that distance.

Effects of preparation procedure on the surface properties of rhodium supported on γ-alumina

The decomposition of rhodium(III) nitrate, chloropentamminerhodium(III) chloride and rhodium(III) sulphite in atmospheres of hydrogen, nitrogen and nitrogen (80%)+ oxygen (20%) have been investigated by thermogravimetric analysis with the salts either pure or impregnated onto a γ-alumina support. The decomposition of rhodium(III) sulphite failed to give dispersions of rhodium metal on alumina but the reduction of the other salts to Rh0 was complete in nitrogen or hydrogen at temperatures between 400 and 690 K.Hydrogen and CO uptake data have shown that rhodium(III) nitrate led to a more finely divided dispersion of metal than did chloropentamminerhodium(III) chloride. Infrared spectra of CO absorbed on the Rh/Al2O3 dispersions were consistent with this conclusion. The effects of sintering and oxygen adsorption on the infrared spectra are reported. Linear and bridge-bonded CO were formed on exposed metal planes or two-dimensional rafts at Rh0 sites which were also active for the chemisorption of oxygen. Gem-dicarbonyl species were formed at monatomically dispersed rhodium sites or edge sites in rafts, both of which had cationic character through interaction with the alumina support. These sites were not active for the adsorption of oxygen.

Infrared study of the interaction between CO and H 2 on ZnO: Mechanism and sites of formation of formyl species

Coadsorption experiments of H 2 or CO with CO 2 show that ZnO sites, previously evidence from CO 2 adsorption experiments, are involved in the reversible adsorption of hydrogen and carbon monoxide. According to our model, H 2 and CO coadsorption leads to hydridozinc carbonyl species. As suggested in homogeneous catalysis, such species are expected to be in equilibrium with formyl species. We show that formyls are indeed formed on ZnO. They are characterized by bands at 2770 and 2661 cm −1 |ν(CH)|, 1520 cm −1 |n(CO)| and 1370 cm −1 |δ(CH)|. In accordance with these results, we show that the amount of reversible species given by H 2, CO and the mixture H 2 + CO (formyl species) is dependent on the ZnO activation temperature T act, 2 variation similar to that observed for linear CO 2 species: it is negligeable when T act < 540 K or T act > 870 K and maximum when T act ≅ 670 K.

Simultaneous measurement of CO oxidation rate and surface coverage on [formula omitted] using infrared spectroscopy: Rate hysteresis and CO island formation

The catalytic oxidation of CO on a commercial Pt Al 2 O 3 catalyst has been studied at a total pressure of one atmosphere using Fourier transform infrared spectroscopy. Simultaneous measurements of steady-state reaction rates and CO surface coverages were obtained at temperatures between 460 and 520 K. During oxidation, the frequency of the infrared absorption peak of linearbonded CO is invariant at 2081 cm −1 at 520 K over nearly a 100-fold change in CO surface coverage. This peak position is within 1 cm −1 of that found for saturation coverage in the presence of pure CO at one atmosphere. In contrast, under nonreactive desorption, large shifts in frequency are found as the CO surface coverage changes. The ratio of the intensities of the absorption bands due to both linear and bridge-bonded CO was constant during oxidation. These observations are interpreted as resulting from the formation of islands of CO during the oxidation reaction. Hysteresis in both CO reaction probability and CO surface coverage are found which are inversely related. Thus CO blocks active sites on the Pt for the reaction. The width and shape of the hysteresis loops as a function of temperature are qualitatively understood in terms of the rate of CO desorption from the Pt surface. At very high surface coverages, changes in the reaction probability are not accompanied by changes in adsorbed CO. This may be due either to the formation of surface species, unobserved in ir, which block the reaction or to the presence of a small number of very reactive Pt sites which are blocked with only a very small change in CO surface coverage.

Effect of temperature on the ventilation response curve to carbon dioxide in anaesthetized cats

Effects of body temperature on the ventillatory control system were studied in 17 anaesthetized cats. At different body temperatures (stabilized within 0.1 °C) CO 2 response curves were measured in each cat. In with chloralose-urethan anaesthetized cats it was found that in the body temperature range of 34–40 °C, in which neither shivering nor panting occurred, no statistically significant trend with temperature was found in the slope (S) and the extrapolated intercept on the Pa CO 2 -axis (B) of the linear CO 2 response curve during hyperoxia as well as hypoxia. In two with pentobarbital anaesthetized cats similar results were obtained. The resting ventilation (at F i CO 2 = 0 ) did not change significantly, while the resting Pa CO 2 during hyperoxia showed a trend to increase with temperature just reaching the level of significance ( P < 0.05). Breathing frequency increased significantly with temperature ( P < 0.0005). When body temperature was elevated above 41 °C both the slope (S) and the intercept of the CO 2 response curve (B) decreased. In three cats ventriculo-cisternal perfusion was performed and no apparent influence of body temperature was found on the relation between the Pcsf CO 2 and on the V̇e-Pcsf CO 2 response curves. These findings show that body temperature has no important modifying effect on the ventilatory responding to CO 2 in anaesthetized cats in the temperature range of 34–40 °C.

Infrared spectroscopic study of CO and CO2 adsorption on Rh–ZrO2, Rh–Al2O3 and Rh–MgO

The adsorption states of CO and CO2 on Rh catalysts supported on ZrO2, Al2O3 and MgO were studied using i.r. spectroscopy. Upon adsorption of CO on reduced Rh–ZrO2, the carbonate bands due to the reaction 2CO →C + CO2, together with the bands of twin, linear and bridge CO species were observed at moderate temperatures, whereas Rh–MgO gave no appreciable formation of CO2 even at higher temperatures (> 100 °C) and Rh–Al2O3 showed intermediate behaviour. On the adsorption of CO2, the linear CO band was formed at lower frequency than that on CO adsorption. The linear CO species formed from CO2 showed higher reactivity toward hydrogen compared with that from CO adsorption.

Surface characterization of supported PtPd bimetallic clusters using infrared spectroscopy

The chemisorption of CO on a series of silica-supported PtPd bimetallic samples has been studied. Using simple mathematical arguments to relate the absorbances of CO adsorbed on Pt and on Pd to metal compositions, we find no evidence of surface enrichment of either metal. Measurements of the H 2 CO uptake ratio suggest that bimetallic-cluster formation inhibits H 2 absorption. Exposure to oxygen followed by rereduction in hydrogen results in the formation of Pd-rich particles, as evidenced by an increase in hydrogen adsorption. Using a theory originally developed by Sachtler, we find that the decrease in intensity of the bridged PdCO bands relative to the linear PdCO bands may be due not only to geometric effects (including short-range ordering), but also to a ligand effect. Most bands in the bimetallic systems are also shifted to lower frequencies. This is another ligand effect and may be explained by the coherent potential theory of alloy formation.

ChemInform Abstract: NOVEL COMPOUNDS WITH GOLD‐TRANSITION METAL BONDS; CRYSTAL AND MOLECULAR STRUCTURE OF BIS(TRIPHENYLPHOSPHINE)IMINIUM BIS(TETRACARBONYLCOBALTIO)AURATE(I)

AbstractBeim Mischen äquimolarer Mengen des Gold‐Komplexes (I) mit den Carbonylmetallaten (II) bzw. (IV) erfolgt rascher Austausch des Tetrahydrothiophens durch die Anioner von (II) und (IV) unter Bildung der neuen Komplexe (III) bzw. (V) mit einer Metall‐ Metall‐Bindung.

Novel compounds with gold–transition–metal bonds; crystal and molecular structure of bis(triphenylphosphine)iminium bis(tetracarbonylcobaltio)aurate(I)

The tetrahydrothiophen group (tht) in [Au(C6F5)3(tht)] can readily be replaced by carbonylmetallate anions [M(Co)n]–(M = Co, n= 4; M = Mn, n= 5) or [M(cp)(CO)3]–(M = Mo or W; cp =η-C5H5) to give a novel type of anionic complex of general formula [N(PPh3)2][(C6F5)3Au–M(CO)n] or [NBun4][(C6F5)3Au–M(cp)-(CO)3] whose reactivity with PPh3 depends upon M. Thus, for M = Mo or W the reaction leads to the cleavage of the metal–metal bond, for M = Mn no reaction is observed at room temperature, whilst substitution of one CO group takes place for M = Co. Reaction of the carbonylmetallates with [Au(C6F5)(tht)] gives rise to disproportionations affording Q[Au(C6F5)2][Q = N(PPh3)2+ or NBun4+] and [N(PPh3)2][Au{M(CO)n}2] or [NBun4]-[Au{M(cp)(CO)3}2] which are stable at room temperature. The presence of the linear unit CO–Au–Co in [N-(PPh3)2][Au{Co(CO)4}2] has been established by a single-crystal structure determination; space group P, a= 9.610(4), b= 9.978(4), c= 11.506(5)Å, α= 97.70(2), β= 97.84(2), γ= 90.97(2)°, and Z= 1. The structure has been refined to R= 0.032 for 2 475 unique observed reflections. Both the anion and cation lie on crystallographic centres of symmetry, hence the Co–Au–Co and P–N–P moieties are linear. The Au–Co bond length is 2.509(2)Å.