Huahua Zhao

One-pot synthesis of ordered mesoporous zirconium oxophosphate with high thermostability and acidic properties

A series of mesoporous zirconium oxophosphate (M-ZrPO) with different P/Zr molar ratios (0–1.25) has been prepared via a facile one-pot evaporation-induced self-assembly (EISA) strategy. After removing the structure-directing agents, the M-ZrPO with large specific surface area (160 m2 g−1), big pore volume (0.26 cm3 g−1) and narrow pore size distribution (5.64 nm) has been obtained. Small-angle X-ray diffraction (SXRD) and transmission electron microscopy (TEM) results showed that these materials had ordered mesoporous structure. With the increase of P/Zr, the textural properties of M-ZrPO could be improved. Moreover, the ordered mesostructure could be maintained even when treated at 800 °C, indicating the M-ZrPO had attractive thermal stability. NH3-TPD and pyridine-IR analyses showed the presence of abundant Bronsted and Lewis acid sites in the material. The M-ZrPO has been used successfully as solid acid catalyst and showed excellent performance in the ketalization reaction.

One-pot synthesis of mesoporous ZrPW solid acid catalyst for liquid phase benzylation of anisole

Mesoporous zirconium phosphotungstate (M-ZrPW), with large specific surface area (~170 m2 g−1), large pore volume (~0.25 cm3 g−1), uniform pore size distribution (~6.5 nm) and tunable W/Zr ratios (0–0.2), was successfully prepared via a facile one-pot evaporation-induced self-assembly (EISA) strategy. Small-angle X-ray diffraction (SXRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) characterizations showed that these materials had a mesoporous structure even when the W/Zr ratio reached up to 0.2. The tungsten species introduced via this strategy highly were dispersed among the wall of mesoporous framework. More importantly, the tungsten species greatly improved the Bronsted acidic property and catalytic activity in the Friedel–Crafts benzylation reaction. The highest activity was obtained at a W/Zr ratio of 0.2 with the strongest Bronsted acidity. In addition, the influences of various reaction parameters such as reaction time, amount of catalyst and calcination temperature of the catalyst, systematically investigated in this paper. Furthermore, the M-ZrPW showed a higher catalytic activity than H-Beta, H-ZSM5 and ZrPW prepared by the sol–gel method. Meanwhile, M-ZrPW could be reused at least for five cycles in the benzylation reaction without any notable decrease of catalytic activity.

Preparation of Cu/ZnO/Al2O3 Catalyst for CO2 Hydrogenation to Methanol by CO2 Assisted Aging

Abstract A Cu/ZnO/Al 2 O 3 catalyst prepared by adding CO 2 during the aging step was used for methanol synthesis from CO 2 and H 2 . The catalysts were characterized by N 2 adsorption-desorption, X-ray diffraction, field emission scanning electron microscope, temperature-programmed decomposition, and temperature-programmed reduction. The precursor from the modified method with added CO 2 had malachite and hydrotalcite-like phases and was more stable than that of the sample without added CO 2 . After calcination, the modified catalyst had a higher surface area, larger pore volume, and smaller particle size. The modified catalyst gave a higher activity for methanol synthesis from CO 2 hydrogenation in the reaction temperature range of 200-260 °C.

Ordered mesoporous zirconium oxophosphate supported tungsten oxide solid acid catalysts: the improved Brønsted acidity for benzylation of anisole

A series of WO3 supported on ordered mesoporous zirconium oxophosphate (X wt% WO3/M-ZrPO) solid acid catalysts with a WO3 loading from 5 to 30 wt% were successfully synthesized, and their structure properties were characterized by X-ray diffraction (XRD), Raman spectroscopy, N2-physisorption, transmission electron microscopy (TEM), UV-visible diffuse reflectance spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, H2 temperature-programmed reduction (H2-TPR) and X-ray photoelectron spectroscopy (XPS). The catalytic performance of X wt% WO3/M-ZrPO in liquid phase benzylation of anisole was studied and the relation between activity and states of tungsten species was investigated detailedly. The maximum catalytic activity was reached at a 20 wt% WO3 loading, which possessed highly dispersed WO3 species and the strongest Bronsted acidity. Meanwhile, the well dispersed WO3 species strongly interacted with M-ZrPO, therefore, both sintering and leaching of WO3 species were effectively restrained. Moreover, compared with the traditional zirconium phosphate synthesized from the sol–gel method (ZrPsol–gel), the M-ZrPO with an abundant ordered mesostructure was propitious for improving the dispersion of WO3 species and catalytic performance. In addition, the 20 wt% WO3/M-ZrPO showed a markedly higher catalytic activity than H-ZSM5, H-Beta and 20 wt% WO3/ZrPsol–gel. Furthermore, the catalyst showed no discernible loss in activity or selectivity after five cycles.

One-pot synthesis of ordered mesoporous transition metal–zirconium oxophosphate composites with excellent textural and catalytic properties

A series of ordered mesoporous transition metal–zirconium oxophosphate composites (M–X–ZrPO, X = Cr, Mn, Fe, Co, Ni, Cu, Zn) were designed and synthesized via a facile and general one-pot evaporation-induced self-assembly (EISA) method. N2-physisorption and TEM characterization showed that all the final materials possessed ordered mesoporous structure accompanied by large specific surface area (170–220 m2 g−1), big pore volume (0.2–0.4 cm3 g−1) and uniform pore size (5.6–7.8 nm). Moreover, the introduced transition metals homogeneously dispersed in the mesoporous skeleton and effectively improved the mesostructure. The catalytic performance of M–X–ZrPO was evaluated in the liquid phase oxidation of ethylbenzene. The introduced transition metals obviously enhanced the catalytic performance of M–ZrPO. M–Mn–ZrPO showed excellent catalytic activity with 91.6% conversion of ethylbenzene and 87.0% selectivity of acetophenone. After five cycles, there was no notable decrease in catalytic activity. Therefore, it was a promising catalyst for the oxidation of ethylbenzene.

Isobutane dehydrogenation over chromia alumina catalysts prepared from MIL-101: Insight into chromium species on activity and selectivity

Abstract Various mesoporous chromia alumina catalysts were prepared by five different methods based on a metal-organic framework MIL-101 and their catalytic performances over isobutane dehydrogenation were investigated. The highly dispersed chromium species were produced on catalyst KCrAl-I 1 with largest specific surface area of 198 m 2 ·g −1 prepared with aluminium isopropoxide (Al( i -OC 3 H 7 ) 3 ) by ultrasonic impregnation method. However, the catalyst KCrAl-I 2 synthesized by stirring impregnation possessed crystalline α-Cr 2 O 3 phase, which was poorly dispersed. Two types of Cr-rich and Al-rich Cr x Al 2– x O 3 solid solutions, designated as CrAl-I and CrAl-II phase, were formed over the catalysts KCrAl-I 3 (prepared by Al( i -OC 3 H 7 ) 3 with nitric acid regulation), KCrAl-C 4 (prepared by aluminium chloride hexahydrate) and KCrAl-N 5 (prepared by aluminium nitrate nonahydrate). Catalytic evaluation results revealed that KCrAl-I 1 exhibited the high isobutane conversion due to its highly dispersed chromium species. However, KCrAl-I 3 , KCrAl-C 4 and KCrAl-N 5 showed the higher isobutene selectivity (95.2 %–96.4%) on account of the formation of chromia alumina solid solutions in the catalysts. Moreover, the solid solution over the chromia alumina catalysts could greatly suppress the coke formation.

Insight into the structure and molybdenum species in mesoporous molybdena–alumina catalysts for isobutane dehydrogenation

The relationship between the structure and Mo species in mesoporous molybdena–alumina catalysts and their catalytic performance for isobutane dehydrogenation has been investigated in detail. Characterization by XRD, HAADF-STEM, EDX, FT-IR, and N2 physisorption illustrated that ordered mesoporous catalysts (OM-Al, MoAl(F), and MoAl(C)) possessed an amorphous alumina phase and non-ordered mesoporous catalysts (M-Al and MoAl) exhibited a γ-Al2O3 phase. Mo species were highly dispersed over all the catalysts because Mo surface densities were about 1.0 Mo nm−2. Moreover, XPS and ICP-OES showed that Mo species were uniformly distributed over MoAl(F) with the Mo species confined in the ordered mesoporous structure. Higher dehydrogenation stability and a lower coke formation rate, albeit lower catalytic conversion, was obtained over MoAl(F) in comparison with those of MoAl(C) and MoAl on account of its stronger metal–support interaction, as shown by H2-TPR technique. The catalyst with a γ-Al2O3 phase exhibited stronger acidity and higher activity than the corresponding catalyst with an amorphous phase. The acidity of the catalysts was greatly enhanced by the addition of Mo species, according to the NH3-TPD characterization. However, not all the acid sites were active sites for dehydrogenation activity. The moderately and strongly acidic sites and the Mo species, including Mo6+ and lower valence Mo species, probably contributed to the dehydrogenation reactivity. Moreover, deactivation of the catalysts was mainly due to coke formation over the spent catalysts.

Precursor effect on the property and catalytic behavior of Fe-TS-1 in butadiene epoxidation

The effect of iron precursor on the property and catalytic behavior of iron modified titanium silicalite molecular sieve (Fe-TS-1) catalysts in butadiene selective epoxidation has been studied. Three Fe-TS-1 catalysts were prepared, using iron nitrate, iron chloride and iron sulfate as precursors, which played an important role in adjusting the textural properties and chemical states of TS-1. Of the prepared Fe-TS-1 catalysts, those modified by iron nitrate (FN-TS-1) exhibited a significant enhanced performance in butadiene selective epoxidation compared to those derived from iron sulfate (FS-TS-1) or iron chloride (FC-TS-1) precursors. To obtain a deep understanding of their structure-performance relationship, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Temperature programmed desorption of NH3 (NH3-TPD), Diffuse reflectance UV–Vis spectra (DR UV–Vis), Fourier transformed infrared spectra (FT-IR) and thermal gravimetric analysis (TGA) were conducted to characterize Fe-TS-1 catalysts. Experimental results indicated that textural structures and acid sites of modified catalysts as well as the type of Fe species influenced by the precursors were all responsible for the activity and product distribution.

The chemoselective hydrogenation of crotonaldehyde over PtFe catalysts supported on La2O2CO3 nanorods

The PtFe catalysts supported on the La2O2CO3 nanorods with various Fe loadings are constructed at the atomic level. The composition and structure of the resultant catalysts are analyzed by ICP-OES, XRD, TEM, H2-TPR, H2-TPD and XPS techniques. A subsequent study of crotonaldehyde hydrogenation over the catalysts shows that the iron addition exerts great influence on the catalyst structure and the associated reactive performance. The surface oxygenated groups of La2O2CO3 afford a high dispersion of Pt due to the interfacial confinement effect. The Pt-support interfaces are wrecked by Fe atoms located on the catalyst surface, simultaneously producing bimetallic surfaces. Both surface studies and catalytic reaction experiment on the catalysts illustrate that an increased electronic density on Pt and the structure evolution of metal particles upon Fe addition is tentatively proposed to be accounted for the distinct catalytic behaviors. Under the working conditions, the highest selectivity toward the desired crotyl alcohol of the Fe-promoted catalysts is two-fold higher than that of the Pt/La2O2CO3.

Insight into the structure evolution and the associated catalytic behavior of highly dispersed Pt and PtSn catalysts supported on La2O2CO3 nanorods

The current work introduces highly dispersed Pt and PtSn catalysts supported on La2O2CO3 nanorods prepared via ultrasonic impregnation, which are used as probe catalysts for the liquid-phase crotonaldehyde hydrogenation. The physicochemical properties of the catalysts are assessed by means of various techniques, including XRD, TEM, XPS, H2-TPD, in situ CO-DRIFT and X-ray adsorption fine structure (XAS). A close combination of catalyst surface experiments and the reactive performances reveals that the distinct reactive performance of the Pt and PtSn catalysts is tentatively attributed to the composition-dependent architecture of Pt–lanthanum interfaces and bimetallic particles while excluding the particle size effect. Catalytic activity tests demonstrate that incorporation of Sn into Pt catalyst brings great significance to the selective hydrogenation of carbonyl groups as it results into the structure evolution of bimetallic particles. An optimization of Sn loading and reaction conditions achieves a 5-fold and 7-fold improvement in the selectivity and yield to crotyl alcohol over the parent Pt catalyst. Lastly, it is found from the catalyst reusability study that metal particles of PtSn catalysts suffers easily from particle migration and growth compared to the Pt catalyst, most likely resulting from a weaker metal–support interaction.