Activity In Ethanol Conversion Research Articles

Effect of large d0 cation doping on gamma‐alumina's acid–base and catalytic properties

AbstractBACKGROUNDCatalysts based on alumina‐supported metal oxides are of crucial importance in the field of heterogeneous catalysis for several applications requiring tuning of surface acidity.RESULTSIn this work, the effects of K+, Ca2+ and La3+ cation doping have been evaluated on a well‐characterized commercial γ‐Al2O3 through morphological characterization and surface characterization (Brunauer–Emmet–Teller, X‐ray diffraction, field emission scanning electron microscopy, Fourier transform infrared spectroscopy). The conversion of ethanol as a test reaction was performed over these catalysts. The impregnated oxide species essentially remain at the surface, resulting in the partial poisoning of the strongest alumina Lewis acid sites. Moreover, oxide anions may increase basicity at the surface. The doping results in a significant decrease in catalytic activity in ethanol conversion to diethyl ether and to ethylene, which is shifted at higher temperatures. On the other side, higher activity in the formation of C4 olefins was detected, namely on the K‐doped alumina.CONCLUSIONThe partial poisoning of the strongest alumina Lewis acid sites and the presence at the surface of new more basic cation–anion couples result in significant changes in catalytic ethanol conversion. © 2023 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).

Acido-basicity of lanthana/alumina catalysts and their activity in ethanol conversion

Lanthana on alumina samples (0.2, 0.8 and 4.7 theoretical monolayers) were prepared by incipient wetness impregnation using γ-Al2O3 as support. Characterization has been performed by BET, XRD, skeletal FT-IR, DR-UVvis, XPS, HR-TEM, IR spectra of the surface OH, adsorbed pyridine and CO2, and isopropanol TPD. Ethanol conversion was investigated both in temperature-programmed surface reaction (TPSR) dynamic conditions as well as in steady-state flow reactor tests. Lanthanum addition stabilizes alumina with respect to sintering and loss of surface area and La- containing phases are observed only for the high-La loaded catalyst. La-alumina catalysts are less active in ethanol dehydration than alumina but more selective to diethyl ether at partial conversion. 5%La2O3/Al2O3 is also equally or more selective than alumina to ethylene at high conversion, producing less carbonaceous material during reaction. Thus, this catalytic system might be a good candidate for (bio)ethylene production through (bio)ethanol dehydration.

Ethanol dehydration on silica-aluminas: Active sites and ethylene/diethyl ether selectivities

Commercial silica-alumina catalysts prepared by different procedures have been characterized. Both present strong Lewis acidity together with Brønsted sites able to protonate pyridine. No evidence of “zeolitic” bridging OH's but significant heterogeneity of terminal silanol groups, part of which are likely “pseudobridging”, was found. Similar high activity in ethanol conversion but markedly different selectivities to ethylene and diethyl ether were found. They are less active than both zeolites and γ-Al2O3. Lewis sites with alumina-like acidobasic neighbor are more selective for ethylene production while Lewis sites with silica-like covalent neighbor are more selective for diethyl ether.

Synthesis of the new framework phosphates and their catalytic activity in ethanol conversion into hydrocarbons

The series of new framework phosphate catalysts was synthesized and their activity in ethanol conversion to hydrocarbons was studied for the first time. The results were summarized for studies of NASICON (NZP) type phosphates formation A1±xZr2−xMx(PO4)3 (where A=H3O+, Li+, Na+, Cu0.5+, M=In, аt x=0, 0.2) with the desired structure and properties controllable by variation of their chemical composition and synthesis parameters. The surface characteristics and catalytic properties of the resulting systems and the yields of the target products formed by ethanol transformations in inert atmosphere were analyzed on the basis of catalysts synthesis conditions. NaZr2(PO4)3 was the most active in hydrocarbons C3+ formation. On benzene yield the catalysts formed the row LiZr2(PO4)3 {II}≈Li1.2Zr1.8In0.2(PO4)3 {II}>LiZr2(PO4)3 {I}>NaZr2(PO4)3 {I}.

Oxidation of ethanol over supported manganese catalysts—effect of the carrier

MnOx catalysts supported on alumina, titania or yttria-stabilised zirconia were studied in ethanol oxidation. Catalysts were characterized by determining their XRD, TPR, TPD-O2 and TPD-NH3 properties and light-off behavior. The effect of kind of carrier on activity in the ethanol oxidation and on selectivity to acetaldehyde (ACA) was determined. Relation between the TPR properties of the catalysts and their activity in ethanol conversion is suggested. The maximum of selectivity to ACA appears in the same sequence of temperatures as the first peak of oxygen desorption from supported MnOx catalysts.

Catalytic conversion of ethanol over Co 3O 4/MgO system treated with γ-irradiation

The catalytic conversion of ethanol over Co 3O 4/MgO system was conducted at temperatures that ranged between 250 and 400 °C using microcatalytic pulse method, with the extent of cobalt oxide varied between 4.76 and 16.70 mol%. The prepared catalyst samples precalcined at 500 °C were subjected to different doses of γ-irradiation that ranged between 0.2 and 1.6 MGy. The results obtained revealed that γ-irradiation resulted in progressive increase in specific surface area to an extent proportional to the absorbed dose of γ-irradiation. This treatment resulted in a progressive decrease in the degree of crystallinity and particle size of Co 3O 4 phase. The employed MgO supported material precalcined at 500 °C exhibited no detectable catalytic activity in ethanol conversion at temperatures reaching 400 °C. On the other hand, all Co 3O 4/MgO samples exhibited convenient catalytic activity and acting as dehydration catalysts. The catalytic activity of the catalysts investigated increased by increasing the extent of cobalt oxide present and also by increasing the dose of γ-irradiation. These results were discussed in terms of an effective increase in the concentration of the catalytically active constituent taking part in the dehydration reaction via decreasing the particle size of cobalt oxide phase.

Synthesis and reactivity of copper-containing nonstoichiometric spinel-type catalysts

Copper-containing nonstoichiometric spinel-type (NSS ) catalysts can be obtained by the calcination of coprecipitated precursors, having a high Cr or Al content. TPR tests indicate the formation of very stable Cu 2+ ions up to a Cu/Cu+Zn ratio of 0.5 and 0.2 for Cr- and Al-containing samples, respectively. These ions may be identified as Cu 2+ ions present in the spinel-type phase or strongly interacting with it. However, increasing the copper content seems to kinetically hinder the reduction of Al-containing samples. Furthermore, traces of either chromate or carbonate phases were found. The NSS catalysts have a very high catalytic activity in ethanol conversion, mainly to acetaldehyde, however, consistent fractions of other products (acetone, methylethyl ketone and ethylacetate) were also observed, especially for the catalysts with higher copper contents. The trivalent element influences the selectivity in these products, chromium favouring the formation of ketones and aluminum that of esters.