Kegong Fang

CuFe, CuCo and CuNi nanoparticles as catalysts for higher alcohol synthesis from syngas: a comparative study

Higher alcohol synthesis (HAS) from syngas has attracted much attention and Cu-modified Fischer–Tropsch (FT) catalysts exhibited promising catalytic performance for HAS. In this paper, three model modified FT catalysts, CuFe, CuCo and CuNi nanoparticles, were synthesized by co-reduction method for the comparison of their performance in HAS. XRD, TEM and EDS characterizations for spent samples indicate that severe phase separation of Cu and Fe took place for CuFe, and Cu@Co core–shell structure formed with co-existence of Cu–Co alloy nanoparticles for CuCo, but only Cu–Ni alloys were observed for CuNi. Such structural change led to different performance in higher alcohol synthesis. As a result, CuFe mainly kept the original FT property of Fe, CuCo showed different performance from Co, and CuNi performed as methanol catalyst.

Advances in bifunctional catalysis for higher alcohol synthesis from syngas

Abstract Bifunctional catalysis on dual sites plays an important role in higher alcohol synthesis from syngas. It makes use of two types of active sites of which one type dissociates CO and forms surface alkyl species and the other type catalyzes non-dissociative CO adsorption for CO insertion and alcohol formation. To improve catalytic activity for higher alcohol synthesis, it is necessary to design dual sites on the atomic scale to give them high stability. The recent advances in higher alcohol synthesis using bifunctional catalysts are reviewed. The design of the dual sites, the structure of the dual sites on several typical catalyst systems, and the structural evolution of the dual sites during reaction are discussed using our latest research results.

n-Dodecane Hydroconversion over Ni/AlMCM-41 Catalysts

Mesoporous aluminosilicate (AlMCM-41) samples were synthesized using various aluminum sources: Al(NO3)3, aluminum isoproxide (Al(OPri)3) and NaAlO2. It was found that the AlMCM-41 prepared using NaAlO2 contained more framework Al(IV) species and stronger acidity compared with those from Al(NO3)3 and Al(OPri)3, respectively. Supported with 2.0 wt% nickel metal, the Lewis acid sites of the AlMCM-41 samples increased due to the compensating effect of the coordinately unsaturated nickel cations, while the Bronsted acid sites slightly decreased because of the coverage of the nickel species. In the n-dodecane hydroconversion, the Ni-containing AlMCM-41 sample prepared by using NaAlO2 gave the symmetrical carbon number distribution and the largest amount of C4–C9 hydrocarbons in the cracked products due to its proper balance between metal and acid functions.

Effect of pore size on the performance of mesoporous zirconia-supported cobalt Fischer–Tropsch catalysts

Mesoporous zirconia with different pore sizes have been prepared and investigated as supports of cobalt catalysts for Fischer–Tropsch synthesis (FTS). It was found that the F–T catalytic performances were closely correlated to the pore sizes of the mesoporous zirconia. The average crystalline sizes of Co3O4 grew with increasing the pore size. Furthermore, their reduction degrees were enhanced, in that the Co–ZrO2 interaction decreased with the increase of pore size. The results from the catalyst testing showed that the FTS catalytic activity, C5+ selectivity, C18+ selectivity and the selectivity to C12–C18 paraffins were enhanced, whereas C1 selectivity decreased with increasing pore size. Based on the systemic study on the effects of the pore sizes of mesoporous zirconia on FTS, it was shown that the Co/PMZ-12 catalyst supported on the large pore size mesoporous zirconia exhibited the largest cobalt oxide particle size, the highest reducibility, and thus showed the highest FTS catalytic activity, with especially good selectivity to C12–C18 paraffins as the main component of the clean diesel oil fraction. The result was attributed to the combination of two factors. One was the improvement of the reducibility of the cobalt catalyst, the control of re-adsorption of the α-alkene and chain growth derived from the large pore size and narrow pore size distribution of the mesoporous support. The other was that the cobalt catalyst supported on zirconia displayed a high FTS catalytic activity and C5+ selectivity.

Higher alcohol synthesis over Cu-Fe composite oxides with high selectivity to C2+OH

Abstract Cu-Fe composite oxides were prepared by co-precipitation method and tested for higher alcohol synthesis from syngas. The selectivity to C 2+ OH and C 6+ OH in alcohol distribution was very high while the methane product fraction in hydrocarbon distribution was rather low, demonstrating a promising potential in higher alcohols synthesis from syngas. The distribution of alcohols and hydrocarbons approximately obeyed Anderson-Schulz-Flory distribution with similar chain growth probability, indicating alcohols and hydrocarbons derived from the same intermediates. The effects of Cu/Fe molar ratio, reaction temperature and gas hourly space velocity (GHSV) on catalytic performance were studied in detail. The sample with a Cu/Fe molar ratio of 10/1 exhibited the best catalytic performance. Higher reaction temperature accelerated water-gas-shift reaction and led to lower total alcohols selectivity. GHSV showed great effect on catalytic performance and higher GHSV increased the total alcohol selectivity, indicating there existed visible dehydration reaction of alcohol into hydrocarbon.

Preparation of nanostructured molybdenum carbides for CO hydrogenation

Novel Mo2C/C nano/microcomposites were prepared via a facile approach involving the hydrothermal carbonization of a solution of glucose as a carbon precursor in the presence of ammonium heptamolybdate tetrahydrate. The samples were subsequently characterized by X-ray diffraction, X-ray photoelectron spectroscopy, thermal gravimetric analysis, N2-physisorption, scanning electron microscopy and high-resolution transmission electron microscopy. The effect of the carbonization agents (Ar, CH4/H2 = 0.2, and H2) was investigated. In particular, the carbonization behaviours and the evolution of Mo species in the catalysts during the carbonization process and the effect on CO hydrogenation for higher alcohol synthesis were extensively studied. During the carbonization step, the catalyst structures experienced an extensive restructuring process, which in turn induced the different performances in the higher alcohol synthesis. Moreover, the nanostructured molybdenum carbides synthesized by this method exhibited great performances in CO hydrogenation for higher alcohol synthesis.

Synthesis of higher alcohols over highly dispersed Cu–Fe based catalysts derived from layered double hydroxides

Highly dispersed Cu-Fe based catalysts with Fe/Cu molar ratios ranging from 0.2 to 1 were prepared via thermal decomposition of layered double hydroxides (LDHs) precursors and tested for higher alcohol synthesis (HAS) via CO hydrogenation. The catalysts were characterized using different techniques such as XRD, TEM, XPS, and H2-TPR. It was demonstrated that the Cu and Fe ions were highly dispersed in the brucite-like layers of the LDHs. With increased Fe/Cu atomic ratio, the tetrahedrally coordinated Cu ion content, Cu reduction temperatures, and the spacing of layers initially increase until the Fe/Cu ratio reaches 0.5 and then decrease. In addition to the catalytic evaluation for CO hydrogenation and catalyst characterization, the relationships between the physical-chemical properties of the catalysts and their catalytic performances were also investigated. It was also found that the alcohols/hydrocarbons ratios correlate linearly with the tetrahedrally coordinated Cu ion content. Moreover, higher reduction temperatures of Cu species as well as larger spacing between the layers in the catalyst are favorable for the synthesis of alcohols. The incorporation of a suitable amount of Fe is beneficial for the production of higher alcohols, with the best catalytic performance (alcohol selectivity of 20.77% and C2+ alcohol selectivity of 48.06%) obtained from a Fe/Cu atomic ratio of 0.5.

Effects of metal promotion on CuMgFe catalysts derived from layered double hydroxides for higher alcohol synthesis via syngas

Cu–Mg–Fe–M–O (M = Mn, Zr, and Ce) catalysts derived from layered double hydroxides (LDHs) precursors were prepared using a co-precipitation method and tested for higher alcohol synthesis (HAS) via carbon monoxide hydrogenation. The catalysts were subsequently characterized by N2-physisorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and H2 temperature-programed reduction (H2-TPR). The results show that Mn, Zr, and Ce promoters mainly contribute to the formation of tetrahedrally coordinated copper species, which favor the enhancement of the total alcohol selectivity. The addition of Mn facilitates the interaction between Cu and Fe, which causes the total alcohol selectivity and C2+ alcohol content in the total alcohols increased from 9.82% and 68.85% to 15.1% and 73.14%, respectively. However, the addition of Zr and Ce weakens the Cu–Fe interaction but increases the possibility of contact between Cu and Fe. As a consequence, the total alcohol selectivity is enhanced, while the C2+ alcohol content in the total alcohols is reduced upon Zr and Ce addition. Based on the characterization and catalytic results of the catalysts, a triple-active-site model is proposed to explain the different promoting effects of the three additives.

A novel Cu–Mn/Ca–Zr catalyst for the synthesis of methyl formate from syngas

A novel catalyst comprised of Cu–Mn mixed oxides and CaO–ZrO2 solid base has contributed to a high-performance methyl formate (MF) synthesis from syngas in a slurry reactor. Cu–Mn mixed oxides and mesoporous CaO–ZrO2 solid base were prepared by complexing method and alcohothermal route, respectively, and they were characterized by N2 isotherm adsorption–desorption, XRD, SEM, TEM, XPS and CO2-TPD techniques. Under the optimum reaction conditions of 160 °C, 3 MPa, 3 : 7 for the ratio of methanol to N,N-dimethylformamide, 40 g L−1 Cu–Mn sample, and 30 g L−1 CaO–ZrO2 sample, a low CO conversion of 22.4% was obtained over Cu–Mn/Ca–Zr, whereas the MF selectivity of 82.3% was higher than that of the traditional catalyst (e.g. Cu-catalyst and NaOCH3), which was due to the synergism between Cu–Mn and CaO–ZrO2 samples.

Efficient V2O5/TiO2 composite catalysts for dimethoxymethane synthesis from methanol selective oxidation

A series of V2O5/TiO2 composite catalysts (V2O5–TiO2–Al2O3, V2O5–TiO2–SiO2, V2O5–TiO2–Ce2O3 and V2O5–TiO2–ZrO2) were prepared by an improved rapid sol–gel method and the catalytic behavior for dimethoxymethane (DMM) synthesized from methanol selective oxidation was investigated. The physicochemical properties of catalysts were characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller isotherms (BET), X-ray photoelectron spectroscopy (XPS), hydrogen temperature-programmed reduction (H2-TPR), NH3 temperature programmed desorption (NH3-TPD), infrared spectroscopy of adsorbed pyridine (Py-IR) and transmission electron microscopy (TEM) techniques. The best catalytic performance was obtained on a V2O5–TiO2–SiO2 catalyst with methanol conversion of 51% and DMM selectivity of 99% at 413 K. Furthermore, the V2O5–TiO2–SiO2 catalyst displayed an excellent catalytic stability within 240 h. Results showed that more Bronsted acidic sites were critical to increasing the DMM yield. The activity of V2O5/TiO2 composite catalysts decreased with increasing Bronsted acidity, but the yield of DMM increased with an increasing amount of Bronsted acidic sites. The excellent performance of the V2O5–TiO2–SiO2 catalyst might come from its optimal acidity and redox properties, higher active surface oxygen species, together with more Bronsted acid sites.