Kamil Klier

Catalytic synthesis of methanol from COH2: I. Phase composition, electronic properties, and activities of the Cu/ZnO/M2O3 catalysts

The low pressure methanol synthesis catalysts CuZnO, Cu/ZnO/Al2O3, and Cu/ZnO/Cr2O3 were found to contain a new compound identified as a CuI solution in ZnO, which is also an active component of the above catalysts. Combined X-ray diffraction, optical, and XPS—Auger studies are presented that describe the formation, electronic structure, and surface composition of these catalysts. In particular, the surface of the working catalyst is free of carbon, both in the presence and absence of CO2 in the feed gas. A synthesis mechanism is proposed whereby the CuI centers nondissociatively chemisorb and activate carbon monoxide and the ZnO surface activates hydrogen. Catalyst deactivation in COH2 mixture is explained as the reduction of CuI to inactive copper metal, while the rate enhancing effect of O2, H2O, and CO2 is due to the maintenance of an oxidation potential high enough to keep the copper in the active CuI state. No special pore distribution or presence of crystalline phases such as spinels is necessary for selectivity of the CuZnO catalyst to the formation of methanol.

Partial Oxidation of Methane

Abstract Partial oxidation is a widely used process to convert hydrocarbons and alcohols to valuable oxygen-containing chemicals. Although methane is the simplest hydrocarbon which gives formaldehyde and methanol as partial oxidation products, the direct utilization of these reactions for the manufacture of formaldehyde and methanol has remained extremely difficult. During the 1940s, two processes for the conversion of methane to formaldehyde were developed in Germany [l]. The first process used NO as a catalyst, and a commercial plant using this process was known to have been in operation in Copsa Mica in Romania. The second process used a combination of ozone and barium peroxide as the catalyst. In the current industrial practice, however, methane is converted to HCHO through a three-step process involving high temperature steam reforming, low pressure methanol synthesis, and oxidative dehydrogenation of methanol to formaldehyde, as shown by Unlike steam reforming, direct oxidation does not require ener...

Catalytic synthesis of methanol from COH2: IV. The effects of carbon dioxide

The effects of carbon dioxide on the catalytic synthesis of methanol over the copper-zinc oxide catalysts were investigated for CO2/CO/H2 ratios between 0/30/70 and 30/0/70. A maximum synthesis rate was observed-at CO2/CO/H2 = 2/28/70. At lower concentrations of CO2 the catalyst is deactivated by overreduction and at higher concentrations of CO2 the synthesis is retarded by a strong adsorption of this gas. A kinetic model is presented which quantitatively describes the observed patterns in the indicated range of synthesis gas compositions and at temperatures between 225 and 250 °C. This model is consistent with all physical characteristics of the CuZnO catalysts and corroborates earlier findings that an intermediate oxidation state of the catalyst is its active state. The adsorption enthalpies and entropies for the reactants indicate that carbon dioxide is strongly bound and immobile while carbon monoxide and hydrogen are chemisorbed with intermediate strength and experience a considerable mobility in the adsorbed layer. At concentrations of CO2 greater than 10%, methane is a side product. Mechanistic implications of this finding are that there is a nonselective pathway parallel to the CO hydrogenation; this pathway may involve formate and methoxy intermediates.

Higher alcohol and oxygenate synthesis over cesium-doped Cu/ZnO catalysts

The synthesis of higher (C+2) alcohols and esters has been studied over cesium-doped CuZnO catalysts. Under higher alcohol synthesis conditions, e.g., 583 K, 7.6 MPa, and gas hourly space velocity = 3260 liters (STP)/kg cat/hr with a H2CO = 0.45 synthesis gas, the presence of cesium promoted the formation of higher oxygenates, especially 2-methyl-1-propanol. The yields of products passed through distinct maxima at cesium nominal concentrations of 0.3–0.5%. These nominal concentrations generated optimum surface cesium concentrations of 15–25%. Under the reaction conditions employed, the principal role of cesium was to increase the ethanol synthesis rate and to provide an even greater enhancement in the rate of ethanol conversion to 1-propanol and subsequently to higher alcohols. To obtain insight into the mechanism of the carbon chain growth, e.g., C1 → C2, C2 → C3, and linear versus branched carbon chain growth, a 13C-NMR study of the C2C4 products formed over CuZnO and 0.4 mol% Cs/Cu/ZnO catalysts was performed. Separate injections into the COH2 synthesis gas of methanol and ethanol with natural-abundance 13C and enriched by 13C in specific positions showed that (i) lower alcohols were incorporated into the synthesis to form higher alcohols; (ii) carbon chain growth occurred in a stepwise manner dominated by the addition of oxygenated C1 intermediates at the β carbons of the oxygenated Cn (n ≥ 2) intermediates but also proceeding via linear addition Cn + C1 (n ≥ 1); and (iii) the presence of cesium had a dramatic effect on the reaction mechanism and promoted greatly the synthesis rates. The mechanistic effects of the alkali dopant were most pronounced in the C2 → C3 step. Over the CuZnO catalyst, injection of ethanol produced 1-propanol via linear chain growth, i.e., CH313CH2OH + COH2 → CH313CH2CH2OH. The presence of Cs effected a mechanistic switch and promoted β-carbon addition, CH313CH2OH + COH2 → 13CH3CH2CH2OH. The position of the 13C label in the CH3 group of propanol provides evidence for retention of oxygen associated with the C1 intermediate, formed from COH2, and loss of oxygen associated with the 13CH2OH group of ethanol. Mechanistically, such a retention is favored by a β-ketoalkoxide intermediate that is bonded to the cesium centers via its anionic oxygen. This unique mechanism is termed herein as aldol coupling with oxygen retention reversal and is specific to the presence of the cesium salt dopant. Higher alcohol synthetic steps C2 + C2 and Cn + Cm (n ≥ 3, m = 1, 2, 3) were also analyzed. Both oxygen retention reversal and normal oxygen retention were observed in coupling reactions leading to the higher-molecular-weight products (m + n > 3), and this observation is attributed to steric effects favoring the cis conformation of the β-alkoxide followed by rejection of either of its two oxygens.

Methanol and C2 oxygenate synthesis over cesium doped Cu/ZnO and Cu/ZnO/Al2O3 catalysts: A study of selectivity and 13C incorporation patterns

Cesium formate significantly promotes methanol and C2 oxygenate (methyl formate MF and ethanol EtOH) synthesis over the CuZnO catalyst. 13C NMR analysis of the product obtained from 13CH3OH and 12COH2 shows that MF is formed by direct carbonylation of methanol and EtOH is formed by coupling of oxygenated C1 intermediates originating from methanol. The C1 coupling mechanism overrides various CO insertion paths to ethanol over the present Cs/Cu/ZnO catalyst. The kinetic significance of C1 aldehydic species such as adsorbed formyl and formaldehyde is supported by experimental evidence and theoretical calculations.

Chemisorption of Carbon Monoxide on (110) and (100) Nickel Crystal Faces

Adsorption equilibria, adsorption rates, and exchange rates of carbon monoxide have been investigated on nickel single‐crystal faces of the (110) and (100) orientation using radiotracer techniques. On the clean annealed surfaces, carbon monoxide is uniformly bound, is mobile, and occupies an area of 9 A2 in the saturated layer. The surface equilibria and the kinetic phenomena are both quantitatively accounted for by a theory utilizing the Stockmayer potential and a cell approximation for describing the lateral interaction of the adsorbed molecules. The ion‐bombarded nonannealed surfaces are unstable and heterogeneous. The contaminated surfaces adsorb only minute amounts of carbon monoxide. The chemisorption of CO thus provides a useful criterion for the degree of cleanliness of nickel surfaces.

Water at interfaces: Molecular structure and dynamics

Abstract Recent advances in molecular mechanics and dynamics of water on inorganic surfaces are reviewed. The structures of hydroxylated surfaces and water-hydroxyl adducts, determined by LEED-Auger studies and infrared spectroscopy, are described to a detail only recently resolved. New mechanistic concepts of nucleation and freezing have ensued from the analysis of time-correlation functions, showing that low-frequency angular perturbations dominate the different behavior of water in bulk phases and at surfaces. While the rotational motion of water molecules in the liquid phase can be interpreted as rotation modulated by making and breaking hydrogen bonds with the neighbors, water adsorbed on nucleating catalysis undergoes an irreversible and complete reorientation in a fraction of the rotational period.

Exchange reactions of oxygen between oxygen molecules and solid oxides

A theory is presented which describes the isotope exchange reactions occurring in the system containing oxygen molecules and an oxide. This theory has been tested by the time dependences of the concentrations of O18O18, O16O18, and O16O16 molecules over magnesium oxide.

The specific copper surface areas in Cu/ZnO methanol synthesis catalysts by oxygen and carbon monoxide chemisorption: Evidence for irreversible CO chemisorption induced by the interaction of the catalyst components

Abstract The chemisorption of oxygen and carbon monoxide has been employed to determine the copper metal surface areas of Cu ZnO methanol synthesis catalysts in the compositional range Cu ZnO = 0 100 to 100 0 . The total, reversible and irreversible adsorption capacities for oxygen and carbon monoxide have been measured at 78 and 293 K, respectively. The reversible CO capacities show good linearity with the irreversible O 2 capacities and lie on a line connecting the capacity for pure copper with that, at zero intercept, of pure zinc oxide. Thus, the crystalline copper surface areas in these biphase catalysts have been evaluated from the specific irreversible adsorption of O 2 on pure copper having surface stoichiometry Cu:O = 2:1. The reversible CO Chemisorption also is a measure of the copper metal surface area but irreversible CO Chemisorption is associated with defect sites, attributed to nonmetallic copper species in zinc oxide. A critical comparison with another traditionally employed method, N 2 O decompositive Chemisorption, shows that the low temperature adsorption of O 2 is the preferred, reliable technique for the determination of crystalline copper surface areas.

Higher alcohol and oxygenate synthesis over Cs/Cu/ZnO/M2O3 (M=Al, Cr) catalysts

Surface doping of Cu/ZnO/M{sub 2}O{sub 3} (M = Al, Cr) catalysts prepared from hydrotalcite precursors with cesium (Cs/Cu/ZnO/M{sub 2}O{sub 3}) significantly enhanced to the alcohol synthesis rate under higher alcohol synthesis conditions. With respect to the unsupported Cs/Cu/ZnO catalyst, the product selectivity of the Cs/Cu/ZnO/Al{sub 2}O{sub 3} catalyst was shifted toward methanol, while the Cs/Cu/ZnO/Cr{sub 2}O{sub 3} catalyst maintained a high selectivity toward C{sub 2}{sup +} alcohols. The presence of cesium in the Cu/ZnO/M{sub 2}O{sub 3} catalysts inhibited the synthesis of dimethyl ether. Comparison of the product distributions obtained over the Cs/Cu/ZnO/M{sub 2}O{sub 3} catalysts with those observed over the Cs/Cu/ZnO catalysts indicates that the function of the Cs/Cu/ZnO/Cr{sub 2}O{sub 3} catalyst is similar to that of the Cs/Cu/ZnO in that higher alcohols are synthesized by a stepwise carbon chain growth via a unique aldol coupling with oxygen retention reversal mechanism. The Al{sub 2}O{sub 3}-based catalysts undergo complex structural changes that probably cause occlusion of the Cs dopant, thus resulting in low selectivity to higher alcohols while retaining high activity toward methanol. 23 refs.