Higher Alcohol Selectivity Research Articles

Light alkane oxidation using catalysts prepared by chemical vapour impregnation: tuning alcohol selectivity through catalyst pre-treatment

Heat treating Fe/ZSM-5 under hydrogen leads to high dispersion of Fe species and higher alcohol selectivity in the oxidation of alkanes, as compared to oxygen treated catalysts.

Cu nanoclusters supported on Co nanosheets for selective hydrogenation of CO

Cu nanoclusters supported on Co nanosheets (denoted Cu/Co) were prepared using lysine as a surfactant template. The shape of the Cu/Co catalyst promotes selective hydrogenation of CO, enhancing CO conversion and the selectivity for higher alcohols, and decreasing methane selectivity, which is in marked contrast to current Cu–Co bimetallic nanoparticle catalysts. The distinct functional interface of the Cu(111) surface with face-centered cubic structure with the Co(100) surface with hexagonal closed-packed structure in the Cu/Co catalyst provides a breakthrough in understanding the catalytic nature of metal-metal interactions. The design of this bimetallic catalyst bridges the gap between model catalysts and realistic catalytic applications, and will ultimately allow us to gain a fundamental understanding of the mechanism of syngas conversion to higher alcohols.

High alcohol synthesis (HAS) from syngas over supported molybdenum carbide catalysts

In this work, different kinds of supported molybdenum carbide catalysts have been prepared using temperature programmed carburization method with 20 vol% CH4/H2. Cobalt and potassium were later loaded over the resultant carbides. The catalysts were evaluated on the new alcohols test rig under 70 bar pressure with syngas feed gas with a H2/CO ratio of 2.0 at various temperatures. The carbide catalysts supported over boron-modified Al2O3 produced higher alcohols in significant yields. The best catalyst achieved 46.7 % selectivity to alcohol at 31.8 % conversion of CO. This corresponds to 199.7 g/alcohol/liter of catalyst/hour. In addition, 72.5 % selectivity to alcohol (93.1 % on CO2 free basis) was achieved at lower temperature with a conversion of 14.1 %. Characterization results showed that the boron-modified supports result in smaller molybdenum carbide crystallite size which might be responsible for the high activity. Higher potassium content benefits the high alcohol selectivity, but affects the catalyst activity to some extent.

Investigation of K-promoted Cu-Zn-Al, Cu-X-Al and Cu-Zn-X (X = Cr, Mn) catalysts for carbon monoxide hydrogenation to higher alcohols

In this study, we report the effect of Cu/Zn/Al chemical composition and Zn and/or Al substitution by Mn and/or Cr in K-promoted Cu-Zn-Al catalysts for the hydrogenation of CO to higher alcohols. In terms of higher alcohols, the synthesis yielded preferentially primary 2-methyl branched alcohols with up to five carbon atoms, namely 2-methyl-1-propanol and 2-methyl-1-butanol, together with ethanol and propanol. Variation of the Cu/Zn/Al chemical composition showed that the catalyst with a Cu/Zn atomic ratio of 1 and low Al content (K-Cu45Zn45Al10) exhibits the optimum performance in terms of both activity and selectivity to higher alcohols. High Al contents on the other hand favor methanol production at the expense of higher alcohols. It is postulated that due to its acidic nature, alumina reduces the basic sites on the catalyst, thereby retarding the C1→C2 step. Substitution of Zn and/or Al by Mn and/or Cr was found to reduce activity by ∼50%, probably due to the lower exposed copper surface area as indicated by the formation of larger CuO crystals. In terms of selectivity, the most appreciable changes were recorded for the K-Cu45Mn45Al10 catalyst, where a 50% increase in higher alcohol formation was measured, rendering the catalyst the most selective among the investigated materials. Characterization of the catalysts provided some insight on the beneficial influence of Zn substitution by Mn in the K-Cu45Mn45Al10 sample. Inverse correlation between acidity and higher alcohols selectivity was evidenced, in accordance with the general notion that higher alcohol formation requires basic sites and indicates that reduced acidity is needed for the aldol-type condensation reactions. The replacement of Mn by Zn in K-Cu-Mn-Al reduced acidity and thus promoted the production of the desired higher alcohol products.

Influence of the support and promotion on the structure and catalytic performance of copper–cobalt catalysts for carbon monoxide hydrogenation

This paper focuses on the effect of support and promotion on the structure and catalytic performance of copper–cobalt catalysts for carbon monoxide hydrogenation. Cu–Co catalysts supported by alumina, silica and carbon nanotubes were prepared by co-incipient-wetness impregnation and are compared with CuCoAl catalyst prepared by coprecipitation. Alumina supported catalysts exhibited much higher alcohol selectivity than their counterparts. This phenomenon was attributed to higher metal dispersion and formation of copper cobalt bimetallic species in alumina supported catalysts which seem to be active in this reaction. Addition of promoter (K, Mg, Zr, and Fe) to alumina supported copper–cobalt catalysts results in a slight modification of metal dispersion, reducibility and catalyst basicity. The alcohol selectivity was improved by promotion of the supported Cu–Co catalysts with small amounts of Fe and Zr but depressed by K and Mg.

Catalytic conversion of syngas to mixed alcohols over Zn-Mn promoted Cu-Fe based catalyst

Zn-Mn promoted Cu-Fe based catalyst was synthesized by the co-precipitation method. Mixed alcohols synthesis from syngas was studied in a half-inch tubular reactor system after the catalyst was reduced. Zn-Mn promoted Cu-Fe based catalyst was characterized by SEM-EDS, TEM, XRD, and XPS. The liquid phase products (alcohol phase and hydrocarbon phase) were analyzed by GC–MS and the gas phase products were analyzed by GC. The results showed that Zn-Mn promoted Cu-Fe based catalyst had high catalytic activity and high alcohol selectivity. The maximal CO conversion rate was 72%, and the yield of alcohol and hydrocarbons were also very high. Cu (111) was the active site for mixed alcohols synthesis, Fe2C (101) was the active site for olefin and paraffin synthesis. The reaction mechanism of mixed alcohols synthesis from syngas over Zn-Mn promoted Cu-Fe based catalyst was proposed. Zn-Mn promoted Cu-Fe based catalyst can be regarded as a potential candidate for catalytic conversion of biomass-derived syngas to mixed alcohols.

Correlation patterns and effect of syngas conversion level for product selectivity to alcohols and hydrocarbons over molybdenum sulfide based catalysts

The focus of the present study was to investigate the effect of the operation conditions, space velocity and temperature, on product distribution for a K–Ni–MoS2 catalyst for mixed alcohol synthesis from syngas. All experiments were performed at 91bar pressure and constant H2/CO=1 syngas feed ratio. For comparison, results from a non-promoted MoS2 catalyst are presented. It was found that the CO conversion level for the K–Ni–MoS2 catalyst very much decides the alcohol and hydrocarbon selectivities. Increased CO conversion by means of increased temperature (tested between 330 and 370°C) or decreased space velocity (tested between 2400 and 18,000ml/(gcath)), both have the same effect on the product distribution with decreased alcohol selectivity and increased hydrocarbon selectivity. Increased CO conversion also leads to a greater long-to-short alcohol chain ratio. This indicates that shorter alcohols are building blocks for longer alcohols and that those alcohols can be converted to hydrocarbons by secondary reactions. At high temperature (370°C) and low space velocity (2400ml/(gcath)) the selectivity to isobutanol is much greater than previously reported (9%C). The promoted catalyst (K–Ni–MoS2) is also compared to a non-promoted (MoS2) catalyst; the promoted catalyst has quite high alcohol selectivity, while almost only hydrocarbons are produced with the non-promoted catalyst. Another essential difference between the two catalysts is that the paraffin to olefin ratio within the hydrocarbon group is significantly different. For the non-promoted catalyst virtually no olefins are produced, only paraffins, while the promoted catalyst produces approximately equal amounts of C2–C6 olefins and paraffins. Indications of olefins being produced by dehydration of alcohols were found. The selectivity to other non-alcohol oxygenates (mostly short esters and aldehydes) is between 5 and 10%C and varies little with space velocity but decreases slightly with increased temperature. Very strong correlation patterns (identical chain growth probability) and identical deviations under certain reaction conditions between aldehyde and alcohol selectivities (for the same carbon chain length) indicate that they derive from the same intermediate. Also olefin selectivity is correlated to alcohol selectivity, but the correlation is not as strong as between aldehydes and alcohols. The selectivity to an ester is correlated to the selectivity to the two corresponding alcohols, in the same way as an ester can be thought of as built from two alcohol chains put together (with some H2 removed). This means that, e.g. methyl acetate selectivity (C3) is correlated to the combination of methanol (C1) and ethanol (C2) selectivities.

Mixed alcohols synthesis from syngas over Cs- and Ni-modified Cu/CeO2 catalysts

Cu/CeO2 (cop) was prepared by a coprecipitation method using NH3·H2O as a precipitant (in order to avoid the residues of alkali metals), followed by a boiling process to eliminate NH3 and decompose [Cu(NH3)4]2+ complex. Because the Cu particles in Cu/CeO2 (cop) were much smaller than those in Cu/CeO2 (imp) (prepared by an impregnation method), Cu/CeO2 (cop) showed a higher activity than that over Cu/CeO2 (imp) for the synthesis of mixed alcohols. Moreover, Cu/CeO2 (cop) showed a higher CO conversion than that over the industrial catalyst Cu/ZnO due to the reducibility of CeO2-based compounds. Although either Cu/ZnO or Cu/CeO2 (cop) produced methanol as a dominant product, the STY of higher alcohols (C2+OH) formed over Cu/CeO2 (cop) was much larger than that over Cu/ZnO because CeO2-based compounds could catalyze the synthesis of isobutane from syngas (isosynthesis). When Cs was introduced into the Cu/CeO2 (cop) catalyst, the mass ratio of C2+OH to MeOH in the products greatly increased from 0.13 to 0.71 but the CO conversion decreased slightly. Both the CO conversion and the selectivity for higher alcohols over CsCu/CeO2 (cop) were higher than those over CsCu/ZnO. By introducing Ni (an F–T element) into CsCu/CeO2 (cop), the CO conversion increased from 22.2% to 37.6% and the mass ratio of C2+OH to MeOH in the products increased from 0.71 to 0.85. Therefore, CsNiCu/CeO2 (cop) is an excellent catalyst for the synthesis of mixed alcohols. A slow deactivation was observed over CsNiCu/CeO2 (cop) in the reaction at 573K for 18h. The deactivated catalyst could be regenerated by calcination in air at 723K and followed by reduction in H2 at 573K.

On the performance of a highly loaded Co/SiO 2 catalyst in the gas phase hydrogenation of crotonaldehyde : Thermal treatments—catalyst structure–selectivity relationship

This paper reports on the performance and its relation with the structure of a highly loaded (41 wt.%) Co/SiO 2 catalyst in the gas phase hydrogenation of crotonaldehyde when varying the thermal treatments to which the catalyst precursor has been subjected. The optimum calcination and reduction temperatures were identified where the highest selectivity to crotyl alcohol (around 90%) was obtained with the catalyst calcined at 400 °C and reduced at 350 °C even at conversions as high as 60%. Higher temperature of calcination was found to lower the crotyl alcohol selectivity. Both, lower and higher reduction temperatures will not favour the crotyl alcohol formation. These results were interpreted and correlated with the surface structure of the catalyst which was shown by temperature programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS) analysis. Depending on the thermal conditions imposed, the surface consisted of either Co metal, or coexisting metal and its oxide; structure which favours the high crotyl alcohol selectivity. By TEM analysis, large particles (diameter exceeding 50 nm) were identified after reduction at 350 °C. A global activation energy of 44 kJ/mol was obtained with this catalyst. In the light of the obtained results a discussion on the reaction mechanism involving metal, metal-oxide double sites has been put forward. It was emphasised that, for selective hydrogenation of crotonaldehyde into unsaturated alcohol, Co catalysts compete favourably with platinum based catalysts.

Fabrication And Application Of Zeolite Membranes

ABSTRACTZeolite Membranes Were Prepared On A Porous Ceramic Support By Hydrothermal Synthesis Using Conventional Heating System And Microwave Heating. Naa And T Type Zeolite Membranes Were Highly Selective For Permeating Water Preferentially With The High Permeation Flux, While Silicalite Membranes Exhibited Preferential Organic Compound Permeation From Water Such As Ethanol/Water. Nay And Nax Zeolite Membranes Showed A High Alcohol Selectivity For Several Feed Mixtures With Methanol Or Ethanol And A High Benzene Selectivity For Benzene/Cyclohexane And Benzene/N-Hexane Separation. The Performance Of The Zeolite Membranes Was The Most Favorable One For Pervaporation Membranes Which Have Been Published So Far And A Tubular Type Module Using A Type Zeolite Membrane For Dehydration Of Organic Liquids Has Been Put Into Industrial Operation. The Tubular Type Pervaporation And Vapor Permeation Module Can Produce 99.8 Wt% Ethanol From 600 L/H, 90 Wt% Ethanol Feed At 120 °C. For The Mass Production Of Zeolite Membrane A New Synthetic Method Using A Microwave Heating Is Also Proposed.

Cu/Mn/ZrO2 catalyst for alcohol synthesis by Fischer-Tropsch modified elements

A Cu/Mn/ZrO2 methanol synthesis catalyst modified by Fischer-Tropsch (F-T) element (Ni,Co,Fe) was prepared by an coprecipatation method. The addition of F-T elements had a great effect on the catalyst performance. The higher alcohol selectivity increased greatly compared with that of the Cu/Mn/ZrO2 catalyst when nickel and cobalt were added, while the addition of iron improved the selectivity tohydrocarbon due to the interaction of the F-T element and the Cu/Mn/ZrO2 catalyst.

Preparation of Faujasite membranes and their permeation properties

NaX and NaY zeolite membranes were grown hydrothermally on the surface of a porous cylindrical support. The molar compositions of the starting gel of NaX and NaY zeolite membranes were SiO 2 /Al 2 O 3 =3.6–5.3 ( X ), 25 ( Y ), Na 2 O/SiO 2 =l.2–l.4 ( X ), 0.88 ( Y ), H 2 O/Na 2 O=30–50. X-ray diffraction (XRD) patterns of membranes consist of peaks corresponding to the support and NaX or NaY zeolite. The Si/Al ratio of these NaX and NaY zeolites determined by atomic absorption spectrophotometry was 1.3 and 2.1, respectively. The outer-surface of the porous support was completely covered with randomly oriented, intergrown NaX or NaY zeolite crystals and the thickness of the membrane was about 20–30 μm, judging from the scanning electron microscopy (SEM) observation. Pervaporation and vapor permeation of organic mixtures through NaY and NaX zeolite membranes was investigated. The zeolite membranes showed high alcohol selectivity for several feed mixtures with methanol or ethanol. Furthermore, high benzene selectivity was observed for benzene/cyclohexane and benzene/ n -hexane separation. High perm-selectivity of the zeolite membrane can be attributed to the selective sorption into the membrane.

Synthesis of mixed alcohols from CO2 contained syngas on supported molybdenum sulfide catalysts

The performances of active carbon supported molybdenum sulfide catalysts prepared by different procedures or promoted by different elements in the synthesis of mixed alcohols from CO2 containing syngas were examined. The results showed that high alcohol activity and selectivity could be obtained by employing a rapid drying procedure and employing a H2SH2 stream for (NH4)2MoS4 decomposition. Addition of Co, Cr and Cl to KMoC catalyst led to an increase in the alcohol activity or selectivity. The presence of CO2 in the feed caused a greater amount of water to be produced but reduced the formation of CO2. The product distribution was also strongly influenced by the presence of either CO2 or H2S in the feed. Addition of CO2 reduces the formation of higher alcohols while H2S increases higher alcohol formation.

NaY zeolite membrane for the pervaporation separation of methanol–methyl tert-butyl ether mixtures

NaY zeolite membrane grown hydrothermally on the surface of a porous alumina substrate shows a high alcohol selectivity in pervaporation, a membrane-based liquid separation process, of alcohol–benzene, cyclohexane or methyl tert-butyl ether.

Carbon monoxide hydrogenation selectivity of catalysts derived from ruthenium clusters on acidic pillared clay and basic layered double-hydroxide supports

Acidic pillared clays, e.g. alumina pillared montmorillonite (APM), and basic layered double hydroxides, e.g. hydrotalcite (HT), provide well defined surface environments for dispersing metal-cluster carbonyl complexes. In the present work, FTIR spectroscopic studies have been used to elucidate the surface organometallic chemistry of Ru3(CO)12 on APM and HT. For APM as the support, cluster binding occurs initially by protonation to form H Ru3(CO)12+ cations on the intracrystalline gallery surfaces of the clay. Further reaction results in the grafting of mononuclear sites of the type [Ru(CO)x(OAl)2]n(x= 2, 3) to the pillar surfaces. The reaction of Ru3(CO)12 with HT affords chemisorbed H Ru3(CO)11– anions which can be tranformed to surface-bound [Ru(CO)x(OM)2]n(M = Al, Mg) complexes analogous to the grafted species on APM. The reduction of the grafted complex on both supports results in active ruthenium catalysts for CO hydrogenation. Ru-APM exhibits very high selectivity for isomerized hydrocarbons (branched alkanes and internal alkenes). The isomerized products arise from the unique texture and bifunctional nature of Ru-APM; the clay-embedded ruthenium catalyses Fischer–Tropsch chain propagation, and the intracrystalline Bronsted acidity of the clay host catalyses alkene rearrangements through carbenium-ion mechanisms. In contrast, the Ru-HT system gives very different product distributions containing a high fraction of oxygenates, specifically methanol and lesser amounts of C2–C4 alcohols. The high alcohol selectivity, which is atypical for CO hydrogenation over Ru, is ascribed in part to the inhibition of CO dissociation on the metal particles by decoraments provided by the highly basic support.