Co-reporter:Pei Wang, Gang Fu, and Huilin Wan
ACS Catalysis August 4, 2017 Volume 7(Issue 8) pp:5544-5544
Publication Date(Web):July 20, 2017
DOI:10.1021/acscatal.7b01498
Here we present a comprehensive survey on identification of the active sites for n-butane activation over binary vanadium phosphorus oxides. Density functional theory calculations show that the activity can be spread over all P═O sites through −OP– chain(s). With an increase in the −OP– chain(s), the activities are gradually decayed. We demonstrate that such a tendency can be quantitatively described by the center of P═O lone-pair band (εlp).Keywords: active site; C−H bond activation; DFT; lone-pair band center; PCET; VPO;
Co-reporter:Ming-Xiang Huang;Xin Wu;Xiao-Dong Yi;Guo-Bin Han;Wen-Sheng Xia
RSC Advances (2011-Present) 2017 vol. 7(Issue 24) pp:14846-14856
Publication Date(Web):2017/03/03
DOI:10.1039/C7RA01190C
Co–Al layered-double-oxides (LDOs) derived from inorganic anion (nitrate, carbonate, sulfate and phosphate) pillared Co–Al layered-double-hydroxides (LDHs) were synthesized. These LDO samples exhibited impressive catalytic performances in oxidative dehydrogenation of propane (ODHP) at low temperatures. Characterization techniques such as XRD, TEM, H2-TPR and O2-TPD were used to measure the physicochemical properties of the samples. The results showed that the LDO samples consisted of homogeneously mixed cobalt spinel oxides (Co2AlOx) containing both Co(III) and Co(II). Co(III) instead of Co(II) was linked with the active sites for ODHP at low temperatures. The sulfate and phosphate anions were preserved in the corresponding LDO samples, unlike the nitrate and carbonate pillars. Sulfate (phosphate) around the cobalt decreased the size of the spinel oxide particles more relative to nitrate and carbonate, and so the dispersion of CoOx in the LDO and the selectivity to propylene in ODHP over these catalysts were improved. Both surface adsorbed oxygen species and surface lattice oxygen species were significantly found over the phosphate-pillared LDO, but only lattice oxygen species were available over the sulfate-pillared LDO. Different mechanisms of propane activation were exhibited over these LDO samples for ODHP.
Co-reporter:Hua-Yi Wu, Peng Jin, Yi-fei Sun, Mei-Hua Yang, Chuan-Jing Huang, Wei-Zheng Weng, Hui-Lin Wan
Journal of Molecular Catalysis A: Chemical 2016 Volume 414() pp:1-8
Publication Date(Web):April 2016
DOI:10.1016/j.molcata.2015.12.024
•VPO/CeO2 and VPO/P-CeO2 catalysts have been firstly synthesized for selective oxidation of n-butane.•The nature of the support has a great influence on the structure and property of VPO.•VPO/P-CeO2 showed higher catalytic performance than bulk VPO and VPO/CeO2.Vanadium phosphorus oxide (VPO) catalysts supported on CeO2 and P-modified CeO2 (P-CeO2) have been firstly synthesized for selective oxidation of n-butane to maleic anhydride (MA). The catalysts supported on P-CeO2 showed higher catalytic performance, especially higher MA selectivity than catalysts on pure ceria, and their specific activities (normalized to per unit mass of VPO loading) were also superior to that of bulk VPO. TG, TEM, XRD, Raman, H2-TPR and XPS results revealed that the structure and property of VPO are largely affected by the support. The loaded VPO existed almost wholly as VOPO4 phases on pure ceria, while mainly in the form of (VO)2P2O7 with small amount of VOPO4 phases on phosphorus-modified ceria. Both VPO/P-CeO2 and bulk VPO catalysts have the similar VPO phase structure, but the former showed the enhanced reducibility of V4+ phase. These differences in structure and properties of the catalysts were discussed and related to their different catalytic performances.For the supported catalysts, NH4H2PO4-treatment can change the properties of the supports and thus affect the phase structure of the catalysts and change the catalytic performance.
Co-reporter:Yu-Hui Hou, Wei-Chen Han, Wen-Sheng Xia, and Hui-Lin Wan
ACS Catalysis 2015 Volume 5(Issue 3) pp:1663
Publication Date(Web):February 2, 2015
DOI:10.1021/cs501733r
Methane is the main component of natural gas and shale gas. It is chemically stable, and its activation often requires high temperatures, which lead to its extensive transformation into undesirable products such as CO and CO2. Thus, the development of efficient catalysts for the selective transformation of methane represents a substantial challenge. In this work, we synthesized La2O2CO3 samples with different morphologies (rod- and plate-shapes) at the nanometer scale. We observed that one of the rod-shaped samples exhibited the best catalytic properties among the investigated samples in the oxidative coupling of methane (OCM) at low temperatures (420–500 °C); in addition, its specific activity was 20 times greater than that of any of the other rod-shaped samples. This difference corresponded to the O2-TPD results and was attributed to the crystallographic facets exposed. Among the exposed facets, the (110), (12̅0), and (21̅0) facets had relatively loose atomic configurations that increased the conversion of methane in the OCM. Moreover, these facets were beneficial to the formation of the chemisorbed oxygen species and their moderately basic sites, which improve the selectivity in the OCM.Keywords: lanthanum oxycarbonate; low temperature; morphology; oxidative coupling of methane; structure sensitivity
Co-reporter:Hua-Yi Wu, Hai-Bo Wang, Xin-Hua Liu, Jian-Hui Li, Mei-Hua Yang, Chuan-Jing Huang, Wei-Zheng Weng, Hui-Lin Wan
Applied Surface Science 2015 Volume 351() pp:243-249
Publication Date(Web):1 October 2015
DOI:10.1016/j.apsusc.2015.05.126
Highlights
- •
The addition of Sm leads to great changes in the structure of VPO catalyst.
- •
Sm improves performance of VPO for oxidation of n-butane to maleic anhydride.
- •
Catalytic performance is closely related to structure of VPO catalyst.
Co-reporter:Lingyun Zhou;Yun Zhao;Zhening Chen;Gang Fu;Huilin Wan
Science China Chemistry 2015 Volume 58( Issue 1) pp:156-161
Publication Date(Web):2015 January
DOI:10.1007/s11426-014-5255-z
Spin-polarized density functional theory (DFT) calculations are carried out to determine the site preference of H adsorption on Pd(100) surface and subsurface. We carefully scrutinize the energy difference between different patterns at θ=0.50 ML and confirm the LEED observation that surface adsorption can form c(2×2) ordering structure. On the contrary, we disclose that p(2×1) structure become more favorable than c(2×2) for subsurface adsorption. These site preferences are rationalized via an analysis of the layer and orbital resolved density of states. Furthermore, we propose that the interstitial charge as a key factor determining the preferred H adsorbed site.
Co-reporter:Qihang Lin;Guohui Yang;Qingjun Chen;Ronggang Fan;Yoshiharu Yoneyama; Huilin Wan; Noritatsu Tsubaki
ChemCatChem 2015 Volume 7( Issue 4) pp:682-689
Publication Date(Web):
DOI:10.1002/cctc.201402929
Abstract
A hierarchical meso/macroporous zeolite-supported Co catalyst (Co/ASB) was designed and employed for the direct synthesis of isoparaffins. The hierarchical porous zeolite (ASB) was developed by a steam-assisted crystallization method using alumina-modified meso/macroporous silica as the precursor. Structural characterization indicated that the as-synthesized ASB exhibited nanosized β-zeolite crystallites and a hierarchical meso/macroporous structure. The activity of the Co/ASB catalyst was much higher than that of conventional Co catalysts supported on SiO2 (Co/SiO2) and H-β-zeolite (Co/B). A high isoparaffins selectivity of 30.5 % was obtained from Co/ASB because of the hydrocracking/isomerization of long-chain hydrocarbons at the strong acidic sites of the β-zeolite. Furthermore, as a result of the fast diffusion of syngas in the unique hierarchical pores, the methane selectivity of Co/ASB was lower than that of Co/B.
Co-reporter:Xiao-Zhang Lin, Guang-Chao Li, Chuan-Jing Huang, Wei-Zheng Weng, Hui-Lin Wan
Chinese Chemical Letters 2013 Volume 24(Issue 9) pp:789-792
Publication Date(Web):September 2013
DOI:10.1016/j.cclet.2013.05.013
A series of nanosized cobalt oxide catalysts modified with phosphorus have been synthesized by the sol–gel method and investigated in the oxidative dehydrogenation of propane to propene. With the addition of phosphorus, the crystallite size of the catalyst was largely decreased, while the P species in the catalyst were highly dispersed. Compared to pure cobalt oxide, the P-modified samples showed higher propane conversion and enhanced propene selectivity. Over the PCoO catalyst with a P/Co atomic ratio of 0.05, the maximal propene yields of 15.7% with a propane conversion of 28.3% were obtained at 520 °C.Nanosized phosphorus-modified cobalt oxide catalysts were synthesized and proved to be effective for oxidative dehydrogenation of propane to propene.
Co-reporter:Yu-Hui Hou;Yin-Liang Lin;Qi Li; Wei-Zheng Weng;Wen-Sheng Xia
ChemCatChem 2013 Volume 5( Issue 12) pp:3725-3735
Publication Date(Web):
DOI:10.1002/cctc.201300667
Abstract
The direct transformation of methane, such as oxidative coupling of methane (OCM), is a long-standing challenge in methane utilization. Keeping this objective in mind, we explored the dispersion and acid–base effects of the catalysts on OCM. Herein, we prepared a series of La2O3/MgO catalysts by using a modified impregnation method with polyvinylpyrrolidone added to impregnated solutions. The BET, XRD, SEM, and TEM characterizations of the samples confirm that La2O3 dispersion on MgO increases with the addition of polyvinylpyrrolidone and the particles become smaller in size and more uniform in distribution. High catalytic performances (e.g., the C2 yield ≈16 %) of the well-dispersed La2O3/MgO catalysts for OCM are demonstrated at a lower temperature (e.g., 550 °C) and a lower loading (e.g., 1.9 wt %). In addition, with the modification of acid–base properties of the supports, we find that base properties of the supports are responsible for C2 formation and acidic properties of the supports are responsible for COx formation. These properties establish a good correlation of the dispersion and basicity of the catalysts with the catalytic performances of the catalysts for OCM.
Co-reporter:Qihang Lin;Guohui Yang; Xiaonian Li;Yoshiharu Yoneyama; Huilin Wan; Noritatsu Tsubaki
ChemCatChem 2013 Volume 5( Issue 10) pp:3101-3106
Publication Date(Web):
DOI:10.1002/cctc.201300336
Abstract
Fused iron (FI), is a general Fischer–Tropsch synthesis (FTS) catalyst and can be used to convert syngas (CO+H2) into normal hydrocarbons. The syntheses of HZSM-5 or H-β zeolite-shell encapsulated catalysts for FTS have been reported previously, however, conventional zeolite-shell synthesis generally employs an organic template, which is neither economic nor environmentally benign. Here we report the synthesis, without using an organic template, of a millimeter-sized defect-free capsule catalyst covered by a MOR zeolite shell (thickness of 23 μm) on FI pellets. The capsule catalyst (HMOR/FI) exhibited excellent performance for FTS, greatly increasing the selectivity of middle isoparaffins. Compared with the pure FI catalyst, the CO conversion of the HMOR/FI capsule catalyst increased remarkably and the iso/n ratio was almost 8 times that of the pure FI catalyst. This report provides an effective route to synthesize a capsule catalyst, which can reduce costs effectively and is also more environmentally benign than the current conventional zeolite-shell synthesis.
Co-reporter:Yanping Zheng, Lihua Zhang, Shaolin Wang, Ding Ding, Hong Zhang, Mingshu Chen, and Huilin Wan
Langmuir 2013 Volume 29(Issue 29) pp:9090-9097
Publication Date(Web):June 13, 2013
DOI:10.1021/la401256z
VOx/Pt(111), which was grown layer-by-layer and exhibited a well-defined structure, was used as a model catalytic surface to study the intrinsic catalytic activity of Pt, as well as the effect of VOx additive, for the oxidation of propane. A special sample system was designed to ensure a reliable analysis of the trace amount of model catalytic reaction products. The results show that the catalytic activities for the oxidation of C3H8 on the Pt(111) surface as adding VOx are suppressed apparently at temperatures below 400 K, but enhanced significantly at temperatures above 400 K. Maximum reaction rates are achieved at a VOx coverage of about 0.3 ML at the test temperatures of 423 and 473 K. The infrared reflection–absorption spectroscopy (IRAS) results show that the redox property of the VOx–Pt is much better than that of the bulklike VOx. This is confirmed by CO poisoning tests, in that the oxidation of VOx/Pt(111) is significantly suppressed by the coadsorbed CO. The kinetic data demonstrate that there are at least two catalytically active sites, metallic Pt and VOx–Pt interface, for the activation and oxidation of C3H8. The promotion effects of VOx on Pt for the oxidation of C3H8 can be attributed to the synergy between VOx and Pt.
Co-reporter:Xiao-Lian Jing, Qing-Chuan Chen, Chong He, Xue-Quan Zhu, Wei-Zheng Weng, Wen-Sheng Xia and Hui-Lin Wan
Physical Chemistry Chemical Physics 2012 vol. 14(Issue 19) pp:6898-6904
Publication Date(Web):20 Mar 2012
DOI:10.1039/C2CP40086C
The photo-induced formation of peroxide ions on the surface of cubic Ln2O3 (Ln = Nd, Sm, Gd) was studied by in situ microprobe Raman spectroscopy using a 325 nm laser as excitation source. It was found that the Raman bands of peroxide ions at 833–843 cm−1 began to grow at the expense of the Ln3+–O2− bands at 333–359 cm−1 when the Ln2O3 samples under O2 were continuously irradiated with a focused 325 nm laser beam at temperatures between 25–150 °C. The intensity of the peroxide Raman band was found to increase with increasing O2 partial pressure, whereas no peroxide band was detected on the Ln2O3 under N2 as well as on the samples first irradiated with laser under Ar or N2 followed by exposure to O2 in the dark. The experiments using 18O as a tracer further confirmed that the peroxide ions are generated by a photo-induced reaction between O2 and the lattice oxygen (O2−) species in Ln2O3. Under the excitation of 325 nm UV light, the transformation of O2 to peroxide ions on the surface of the above lanthanide sesquioxides can even take place at room temperature. Basicity of the lattice oxygen species on Ln2O3 also has an impact on the peroxide formation. Higher temperature or laser irradiation power is required to initiate the reaction between O2 and O2− species of weaker basicity.
Co-reporter:Wen-Sheng Xia, Yu-Hui Hou, Gang Chang, Wei-Zheng Weng, Guo-Bin Han, Hui-Lin Wan
International Journal of Hydrogen Energy 2012 Volume 37(Issue 10) pp:8343-8353
Publication Date(Web):May 2012
DOI:10.1016/j.ijhydene.2012.02.141
A Ni catalyst supported on mono dispersed silica spheres, Ni/SiO2-Sph (SG), has been successfully synthesized by a sol–gel method. By comparing it with other Ni catalysts (supported on commercial silica and silica spheres) prepared by an impregnation method, we find that the size of Ni particles and their dispersion are closely related to performances of the catalysts in partial oxidation of methane (POM) into synthesis gas (CO + H2). Several means such as H2-TPR, TEM, and XRD are employed to characterize these catalysts. Although the catalyst Ni/SiO2-Sph (SG) in specific surface area is not large, the Ni particles are the smallest in size (3–5 nm) among the three catalysts, and are uniformly distributed, high dispersed over the silica surfaces, being not much changed as Ni loading. It is notable that the smaller size of the NiO particles is corresponding to the stronger NiO–SiO2 interactions. The catalyst Ni/SiO2-Sph (SG) shows the best catalytic performances and the longest lifetime among the three catalysts at the POM conditions.Highlights► Ni catalysts supported on mono dispersed silica spheres have been prepared. ► The catalysts prepared by a sol–gel method show good POM performances & stability. ► The active sites (Ni) are small in size and uniformly distributed on silica. ► The Ni–SiO2 interactions are increased as the size of the Ni particles decreased. ► More numerous Ni particles that interacted with silica are vital to POM stability.
Co-reporter:Ru-Ming Yuan, Gang Fu, Xin Xu and Hui-Lin Wan
Physical Chemistry Chemical Physics 2011 vol. 13(Issue 2) pp:453-460
Publication Date(Web):29 Oct 2010
DOI:10.1039/C0CP00256A
The selective catalytic reduction (SCR) of NO by NH3 over V2O5-based catalysts is used worldwide to control NOx emission. Understanding the mechanisms involved is vital for the rational design of more effective catalysts. Here, we have performed a systematic density functional theory (DFT) study of a SCR reaction by using cluster models. Three possible mechanisms have been considered, namely (i) a Lewis acid mechanism, (ii) a Brønsted acid mechanism and (iii) a nitrite mechanism. Our calculations down-play the significance of mechanism (i) due to its high barrier as well as the incorrect reaction order. On the other hand, our calculations demonstrate that both mechanisms (ii) and (iii) can lead to a first order reaction with respect to NO with the predicted barriers being consistent with the experimental observations. Thus, we conclude: there exists two competitive pathways for SCR. Mechanism (ii) is dominant when the Brønsted acidity of the catalysts is relatively strong, while mechanism (iii) becomes important when Brønsted acidity is weak or absent. Importantly, we demonstrate that the latter two mechanisms share a common feature where N–N bond formation is ahead of N–H bond cleavage, in contrast to that in mechanism (i). Such a sequence provides an effective way to reduce the side reaction of ammonia combustion since the relatively strong N–N bond has already been formed.
Co-reporter:Bing Li; Wei-Zheng Weng;Qing Zhang;Zhao-Wen Wang ; Hui-Lin Wan
ChemCatChem 2011 Volume 3( Issue 8) pp:1277-1280
Publication Date(Web):
DOI:10.1002/cctc.201100043
Co-reporter:Ru-Ming Yuan ; Gang Fu ; Xin Xu
The Journal of Physical Chemistry C 2011 Volume 115(Issue 43) pp:21218-21229
Publication Date(Web):September 26, 2011
DOI:10.1021/jp206265p
Selective catalytic oxidation (SCO) of ammonia to a nitrogen molecule is an important process involved in many applications such as removing NH3 slip in selective catalytic reduction (SCR) of NOx, reducing the NH3 concentration from biomass-derived fuels, etc. Here we perform density functional theory calculations in conjunction with cluster models to investigate the SCO mechanisms on V2O5 surfaces. Our calculations show that, at the initial stage, NH3 can be activated by transferring an electron to the metal oxide surfaces, giving rise to an NH3+ intermediate. We disclose that the subsequent pathways are strongly dependent on the availability of the gaseous species. When oxygen is limited or absent, N2H4 can be produced from NH3+ reacting with a second NH3 or from two activated intermediates (e.g., NH2 + NH2 or ONH2 + NH2), and oxidation of N2H4 into N2 by V═O is viable. On the other hand, when oxygen is abundant, NH3+ will react with O2 to make a NH3+···O2 complex. Such a species will quickly decompose into NO, which switches on the selective catalytic reduction (SCR) reaction, eventually leading to the formation of N2. We propose that the combination of an efficient Ostwald reaction catalyst for NH3 to NO transformation with a capable SCR reaction catalyst for NO reduction by NH3 to N2 can lead to a good candidate catalyst for SCO at the high O2/NH3 ratio condition.
Co-reporter:Yiming He, Ying Wu, Xiaodong Yi, Weizheng Weng, Huilin Wan
Journal of Molecular Catalysis A: Chemical 2010 Volume 331(1–2) pp:1-6
Publication Date(Web):1 October 2010
DOI:10.1016/j.molcata.2010.08.004
A series of MoTeOx/SiO2 and MoBiTeOx/SiO2 catalysts was prepared and catalytic performance of propane partial oxidation to acrolein was tested. The addition of low amount of Bi component to MoTeOx/SiO2 catalysts was found to significantly promote acrolein selectivity. The catalyst structure and redox properties were investigated by means of X-ray powder diffraction, Raman spectroscopy, in situ Raman spectroscopy, X-ray photoelectron spectroscopy, and H2-TPR techniques. Results indicate that the Bi promotive effect can be attributed to two possible reasons. One is that the Bi component promotes the dispersal of MoO3. The isolation effect results in acrolein selectivity increase. Another reason is that Bi doping enhances lattice oxygen diffusion and increases the amount of surface active oxygen, which is responsible for the oxidation of intermediate propylene to acrolein.The doping of Bi promoted the dispersal of MoO3 and enhanced lattice oxygen diffusion, the catalytic performance of MoBiTeOx/SiO2 was thus increased.
Co-reporter:Yiming He;Ying Wu;Xiaodong Yi
Reaction Kinetics, Mechanisms and Catalysis 2010 Volume 99( Issue 1) pp:149-156
Publication Date(Web):2010 February
DOI:10.1007/s11144-009-0125-y
This paper presents the synergetic effect of Te2MoO7 and MoO3 (WO3) in the partial oxidation of propylene to acrolein. The study found that the addition of MoO3 (or WO3) to Te2MoO7 greatly promoted the propylene conversion and acrolein yield. As the results of the investigation revealed, the higher catalytic performance could be attributed to the increased acidity, which is beneficial for the adsorption of propylene.
Co-reporter:Jianhui Li;Caicai Wang;Chuanjing Huang;Weizheng Weng;Huilin Wan
Catalysis Letters 2010 Volume 137( Issue 1-2) pp:81-87
Publication Date(Web):2010 June
DOI:10.1007/s10562-010-0333-0
Nanosized CeNbNiO catalysts have been prepared by a modified sol–gel method and investigated in the oxidative dehydrogenation of propane to propene (ODHP). The addition of Nb into NiO can enhance the propene selectivity, while Ce introduction can largely increase propane conversion at low temperature. With 1.5Ce3NbNiO catalyst, a propene yield of 10.4% was obtained at 250 °C. XRD, N2-adsorption, H2-TPR, XPS, O2-TPD, NH3-TPD and pulse reaction have been performed to study the intrinsic difference between these NiO-based catalysts. A strong interaction between Ni and Ce/Nb species was clearly evidenced for the doped NiO samples. The doped elements affected greatly the catalyst properties such as surface acidity and the reactivity of oxygen species, which are closely related to the catalytic performance of the catalysts.
Co-reporter:Miao Sun, Jizhe Zhang, Qinghong Zhang, Ye Wang and Huilin Wan
Chemical Communications 2009 (Issue 34) pp:5174-5176
Publication Date(Web):21 Jul 2009
DOI:10.1039/B910317A
A Keggin-type polyoxometalate (Cs1.5H1.5PW12O40)-supported Pd catalyst is efficient for the direct synthesis of H2O2 from H2 and O2 in the absence of any acid or halide additives under atmospheric pressure.
Co-reporter:Yao Wang, Gang Fu, Ying Zhang, Xin Xu, Huilin Wan
Chemical Physics Letters 2009 Volume 475(4–6) pp:202-207
Publication Date(Web):25 June 2009
DOI:10.1016/j.cplett.2009.05.044
The mechanism of the gas-phase reaction N2O + CO → N2 + CO2 has been elucidated by means of various density functional methods in conjunction with the ab initio methods. An indirect and step-wise pathway in which CO approaches to the N-end of N2O, is concluded to be lower in energy than an O-end route, which is a direct O-atom transfer pathway initiated by CO approaching to the O-end of N2O. High level ab initio method (i.e. QCISD(T)//QCISD) suggests that MP2 may inappropriately estimate the electron correlation effect, leading to unreasonable geometry and energetics for this reaction.For N2O + CO → N2 + CO2, an N-end route is found lower in energy than an O-end pathway.
Co-reporter:Yubao Zhao, Xiaohong Yuan, Chuanxiang Liu, Chuanjing Huang, Huilin Wan
Materials Letters 2007 Volume 61(4–5) pp:942-943
Publication Date(Web):February 2007
DOI:10.1016/j.matlet.2006.06.018
The phase transformation from tetragonal to monoclinic of zirconia for a series of sulfated zirconia–LiCl samples was characterized by ultraviolet Raman spectroscopy (UVRS) and X-ray diffraction (XRD). Results show that such phase transformation increases with increasing LiCl content and the monoclinic phase is first detected by XRD than that by UVRS for the sample with Li content of 0.5 wt.%. The comparison between XRD and UVRS characterizations indicates that the phase transition takes place initially at the core.
Co-reporter:Fang Ying;Jianhui Li;Chuanjing Huang;Weizheng Weng;Huilin Wan
Catalysis Letters 2007 Volume 115( Issue 3-4) pp:137-142
Publication Date(Web):2007 June
DOI:10.1007/s10562-007-9079-8
V-containing SBA-15 mesoporous materials have been directly synthesized in an acidic and peroxidic medium. Compared to V/SBA-15 and V/SiO2 samples prepared by impregnation method, the materials thus synthesized show larger surface areas, higher dispersion and reducibility of VOx species, and superior catalytic performance for oxidative dehydrogenation of propane.
Co-reporter:Tinghua Wu, Qiangu Yan, Huilin Wan
Journal of Molecular Catalysis A: Chemical 2005 Volume 226(Issue 1) pp:41-48
Publication Date(Web):1 February 2005
DOI:10.1016/j.molcata.2004.09.016
Partial oxidation of methane to hydrogen and carbon monoxide (POM) over a Ni/TiO2 catalyst has been investigated using a fixed-bed reactor. Ni/TiO2 catalyst has high initial activity but undergoes deactivation during POM. Activation of methane on Ni/TiO2 was studied by employing a pulse reaction technique in the absence of gas phase oxygen. Methane pulse reactions demonstrate that the methane oxidation mechanism changes as the nickel oxidation state changes over Ni/TiO2. CH4 is efficiently oxidized into CO and H2 via a direct oxidation mechanism when Ni/TiO2 is reduced; while CH4 may be converted by a non-selective oxidation process over oxidized Ni/TiO2.The methane oxidation mechanism changes as the nickel oxidation state changes over Ni/TiO2. Methane is oxidized by lattice oxygen in NiO by active oxygen in the TiO2 support via the non-selective mechanism over oxidized Ni/TiO2, while it is converted into CO and H2 via a direct oxidation mechanism over reduced Ni/TiO2.
Co-reporter:Wei Zheng Weng;Ming Shu Chen;Hui Lin Wan
The Chemical Record 2002 Volume 2(Issue 2) pp:
Publication Date(Web):15 APR 2002
DOI:10.1002/tcr.10017
In situ time-resolved Fourier transform infrared (FTIR) and microprobe Raman spectroscopies were used to characterize the reaction mechanisms of the partial oxidation of methane to syngas over SiO2- and γ-Al2O3-supported rhodium and ruthenium catalysts. The interaction of both pure methane and a methane/oxygen mixture at a stoichiometric feed ratio with an oxygen-rich catalyst surface led to the formation of CO2 and H2O as the primary products. For the H2-pretreated samples, the reaction mechanisms with the catalysts differ. Only Rh/SiO2 is capable of catalyzing the direct oxidation of methane to syngas, while syngas formation over Rh/g-Al2O3, Ru/SiO2, and Ru/g-Al2O3 can be achieved mainly via a combustion-reforming scheme. The significant difference in the mechanisms for partial oxidation of methane to syngas over the catalysts can be correlated to the differences in the concentration of oxygen species (O2−) on the catalyst surface during the reaction, mainly due to the difference in the nature of the metals and supports. © 2002 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 2:102–112, 2002: Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/tcr.10016
Co-reporter:Meiliu Wang, Weizheng Weng, Haozhuan Zheng, Xiaodong Yi, ... Huilin Wan
Journal of Natural Gas Chemistry (September 2009) Volume 18(Issue 3) pp:300-305
Publication Date(Web):1 September 2009
DOI:10.1016/S1003-9953(08)60126-7
Oscillations in temperatures of catalyst bed as well as concentrations of gas phase species at the exit of reactor were observed during the partial oxidation of methane to synthesis gas over Ru/Al2O3 in the temperature range of 600 to 850 °C. XRD, H2-TPR and in situ Raman techniques was used to characterize the catalyst. Two types of ruthenium species, i.e. the ruthenium species weakly interacted with Al2O3 and that strongly interacted with the support, were identified by H2-TPR experiment. These species are responsible for two types of oscillation profiles observed during the reaction. The oscillations were the result of these ruthenium species switching cyclically between the oxidized state and the reduced state under the reaction condition. These cyclic transformations, in turn, were the result of temperature variations caused by the varying levels of the strongly exothermic CH4 combustion and the highly endothermic CH4 reforming (with H2O and CO2) reactions (or the less exothermic direct partial oxidation of methane to CO and H2), which were favored by the oxidized and the metallic sites, respectively. The major pathway of synthesis gas formation over the catalyst was via the combustion-reforming mechanism.
Co-reporter:Yiming He, Ying Wu, Weizheng Weng, Huilin Wan
Journal of Natural Gas Chemistry (May 2011) Volume 20(Issue 3) pp:249-255
Publication Date(Web):1 May 2011
DOI:10.1016/S1003-9953(10)60194-6
AbstractA detailed study on the synergetic effect of TeMo5O16 and MoO3 phases in the MoTeOx catalysts for the partial oxidation of propylene to acrolein has been reported in this work. It was found that both propylene conversion and acrolein selectivity increased with the addition of MoO3 to TeMo5O16. Based on the results of N2 adsorption-desorption, XRD, XPS, in-situ XRD, O2-TPO, and 2-propanol decomposition reaction, the higher catalytic performance and synergetic effect could be attributed to the enhancement of acidity and the oxygen transfer from TeMo5O16 to MoO3 phase.
Co-reporter:Qihang Lin, Qingde Zhang, Guohui Yang, Qingjun Chen, Jie Li, Qinhong Wei, Yisheng Tan, Huilin Wan, Noritatsu Tsubaki
Journal of Catalysis (December 2016) Volume 344() pp:378-388
Publication Date(Web):1 December 2016
DOI:10.1016/j.jcat.2016.10.012
•A novel palladium-promoted cobalt-based zeolite capsule catalyst was developed.•The main cobalt species in the Pd-promoted capsule catalyst was cobalt silicate.•Pd promoted formation of cobalt silicate during hydrothermal synthesis of zeolite shell.•Pd could improve the reduction in cobalt silicate under traditional reduction condition.•The obtained catalyst exhibited excellent performance for C5–C11 iso-paraffins synthesis.Pd-promoted zeolite capsule catalyst (Co/Pd/SiO2-HZSM5) was developed by coating H-ZSM-5 zeolite shell over Pd-modified core catalyst (Co/Pd/SiO2), and employed for direct synthesis of C5–C11 iso-paraffins from syngas via Fischer-Tropsch synthesis (FTS). The roles of Pd promotion in structure and performance of the capsule catalyst for C5–C11 iso-paraffins synthesis were deeply studied. Structure characterizations (XRD, FTIR, TPR, and XPS) indicated that the main cobalt species in Pd-promoted capsule catalyst was cobalt silicate, while Co3O4 was the predominant cobalt species in un-promoted capsule catalyst (Co/SiO2-HZSM5). Evolution of cobalt species in the synthesis of Pd-promoted capsule catalyst revealed that Pd improved the formation of cobalt silicate in strong basic TPAOH solution during the hydrothermal synthesis of H-ZSM-5 zeolite shell. It was found that Pd not only promoted the reduction in cobalt oxides, but also improved the reduction in cobalt silicate, which could not be reduced under traditional reduction condition for cobalt-based FTS catalysts. Catalytic tests indicated that Pd-promoted capsule catalyst exhibited highly enhanced performance for C5–C11 iso-paraffins synthesis with molar ratio of iso-paraffins to n-paraffins up to 1.03. Long-chain hydrocarbons were completely eliminated in the capsule catalyst as a consequence of spatial confinement effect of the H-ZSM-5 zeolite shell. The hydrogenation of olefins to paraffins, which was enhanced by Pd promotion, together with the hydrocracking and isomerization of primary hydrocarbons, contributed to the high selectivity of C5–C11 iso-paraffins in Pd-promoted capsule catalyst.Download high-res image (186KB)Download full-size image
Co-reporter:Miao Sun, Jizhe Zhang, Chuanjing Cao, Qinghong Zhang, Ye Wang, Huilin Wan
Applied Catalysis A: General (31 October 2008) Volume 349(Issues 1–2) pp:
Publication Date(Web):31 October 2008
DOI:10.1016/j.apcata.2008.07.035
Two series of Keggin-type polyoxometalates (i.e., CsxH3−xPMo12O40 and CsxH4−xPVMo11O40) with different cesium contents have been studied for the oxidative dehydrogenation of propane at a mild temperature (653 K). The conversion of propane decreases while the selectivity to propylene increases with increasing cesium content, and the yield of propylene reaches a maximum at appropriate cesium content for either series of catalysts. The best yield of propylene (9.3%) has been achieved over the CsxH3−xPMo12O40 catalyst with an x value of 2.56, and the vanadium substitution cannot enhance the maximum yield of propylene. The correlation between catalytic behaviors and physicochemical properties of the catalysts suggests that the acidity of the present catalysts plays crucial roles in the oxidative dehydrogenation of propane. It is clarified that the rate of propane conversion increases proportionally to the concentration of Brønsted acid sites, whereas the selectivity to propylene decreases with increasing the surface acidity.Propane conversion decreases while propylene selectivity increases with increasing cesium content in the CsxH3−xPMo12O40 (x = 2–3) and CsxH4−xPVMo11O40 (x = 2–4) catalysts with different cesium contents. We have clarified that the rate of propane conversion increases proportionally to the concentration of surface Brønsted acid sites, whereas the selectivity to propylene decreases with increasing the surface acidity.
Co-reporter:X.X. Gao, C.J. Huang, N.W. Zhang, J.H. Li, W.Z. Weng, H.L. Wan
Catalysis Today (29 February 2008) Volume 131(Issues 1–4) pp:211-218
Publication Date(Web):29 February 2008
DOI:10.1016/j.cattod.2007.10.051
A series of calcium-modified alumina-supported cobalt catalysts were prepared with a two-step impregnation method, and the effect of calcium on the catalytic performances of the catalysts for the partial oxidation of methane to syngas (CO and H2) was investigated at 750 °C. Also, the catalysts were characterized by XRD, TEM, TPR and (in situ) Raman. At 6 wt.% of cobalt loading, the unmodified alumina-supported cobalt catalyst showed a very low activity and a rapid deactivation, while the calcium-modified catalyst presented a good performance for this process with the CH4 conversion of ∼88%, CO selectivity of ∼94% and undetectable carbon deposition during a long-time running. Characterization results showed that the calcium modification can effectively increase the dispersion and reducibility of Co3O4, decrease the Co metal particle size, and suppress the reoxidation of cobalt as well as the phase transformation to form CoAl2O4 spinel phases under the reaction conditions. These could be related to the excellent catalytic performances of Co/Ca/Al2O3 catalysts.
Co-reporter:Jian-Mei Li, Fei-Yang Huang, Wei-Zheng Weng, Xiao-Qing Pei, Chun-Rong Luo, Hai-Qiang Lin, Chuan-Jing Huang, Hui-Lin Wan
Catalysis Today (29 February 2008) Volume 131(Issues 1–4) pp:179-187
Publication Date(Web):29 February 2008
DOI:10.1016/j.cattod.2007.10.040
Catalytic performance for partial oxidation of methane (POM) to synthesis gas was studied over the Rh/Al2O3 catalysts with Rh loadings between 0.1 and 3 wt%. It was found that the ignition temperature of POM reaction increased with the decreasing of the Rh loadings in the catalysts. For the POM reaction over the catalysts with high (≥1 wt%) Rh loadings, steady-state reactivity was observed. For the reaction over the catalysts with low (≤0.25 wt%) Rh loadings, however, oscillations in CH4 and reaction products (CO, H2, and CO2) were observed. Comparative studies using H2-TPR, O2-TPD and high temperature in situ Raman spectroscopy techniques were carried out in order to elucidate the relation between the redox property of the Rh species in the Rh/Al2O3 with different Rh loadings and the performance of the catalysts for the reaction. Three kinds of oxidized rhodium species, i.e. the rhodium oxide species insignificantly affected by the support (RhOx), that intimately interacting with the Al2O3 surface (RhiOx) and the Rh(AlO2)y species formed by diffusion of rhodium oxides in to sublayers of Al2O3 [C.P. Hwang, C.T. Yeh, Q.M. Zhu, Catal. Today, 51 (1999) 93.], were identified by H2-TPR and O2-TPD experiments. Among them, the first two species can be easily reduced by H2 at temperature below 350 °C, while the last one can only be reduced by H2 at temperature above 500 °C. The ignition temperatures of POM reaction over the catalysts are closely related to the temperature at which most of the RhOx and RhiOx species can be reduced by CH4 in the reaction mixture. Compared to the Rh/Al2O3 with high Rh loadings, the catalysts with low Rh loadings contain more RhiOx species which possess stronger RhO bond strength and are more difficult to be reduced than RhOx by the reaction mixture. Higher temperature is therefore required to ignite the POM reaction over the catalysts with lower Rh loadings. The oscillation during the POM reaction over the Rh/Al2O3 with low Rh loadings can be related to the behaviour of Rh(AlO2)y species in the catalyst switching cyclically from the oxidized state to the reduced state during the reaction.
Co-reporter:Li-Hua Wang, Xiao-Dong Yi, Wei-Zheng Weng, Hui-Lin Wan
Catalysis Today (29 February 2008) Volume 131(Issues 1–4) pp:135-139
Publication Date(Web):29 February 2008
DOI:10.1016/j.cattod.2007.10.014
Pulse reaction method and in situ IR spectroscopy were used to characterize the active oxygen species for oxidative coupling of methane (OCM) over SrF2/Nd2O3 catalyst. It was found that OCM activity of the catalyst was very low in the absence of gas phase oxygen, which indicated that lattice oxygen species contributed little to the yield of C2 hydrocarbons. IR band of superoxide species (O2−) was detected on the O2-preadsorbed SrF2/Nd2O3. The substitution of 18O2 isotope for 16O2 caused the IR band of O2− at 1128 cm−1 to shift to lower wavenumbers (1094 and 1062 cm−1), consistent with the assignment of the spectra to the O2− species. A good correlation between the rate of disappearance of surface O2− and the rate of formation of gas phase C2H4 was observed upon interaction of CH4 with O2-preadsorbed catalyst at 700 °C. The O2− species was also observed on the catalyst under working condition. These results suggest that O2− species is the active oxygen species for OCM reaction on SrF2/Nd2O3 catalyst.
Co-reporter:Jing-Dong Xu, Ze-Ying Chang, Kong-Tao Zhu, Xue-Fei Weng, Wei-Zheng Weng, Yan-Ping Zheng, Chuan-Jing Huang, Hui-Lin Wan
Applied Catalysis A: General (25 March 2016) Volume 514() pp:103-113
Publication Date(Web):25 March 2016
DOI:10.1016/j.apcata.2015.12.023
Co-reporter:Ying Liu, Fei-Yang Huang, Jian-Mei Li, Wei-Zheng Weng, Chun-Rong Luo, Mei-Liu Wang, Wen-Sheng Xia, Chuan-Jing Huang, Hui-Lin Wan
Journal of Catalysis (10 June 2008) Volume 256(Issue 2) pp:192-203
Publication Date(Web):10 June 2008
DOI:10.1016/j.jcat.2008.03.009
In situ microprobe Raman and XRD techniques were used to follow the oxidation state of Rh/Al2O3 and Ru/Al2O3 catalysts during the catalytic ignition process of the partial oxidation of methane (POM) to synthesis gas. It was found that the catalyst was in the fully oxidized state before ignition of the POM reaction, and abruptly changed its oxidation state at the temperature at which the POM reaction started. After the POM reaction was ignited, the amount of Rh2O3 or RuO2 in the catalyst at the entrance of the catalyst bed was below the detection level of Raman spectroscopy. Due to the greater MO bond strength of RuO compared with RhO, Ru/Al2O3 demonstrated a greater tendency to oxidize than Rh/Al2O3 under the POM conditions. This factor affects the oxygen coverage on the two catalysts under reaction conditions and consequently affects the pathways of synthesis gas formation.
Co-reporter:Ru-Ming Yuan, Gang Fu, Xin Xu and Hui-Lin Wan
Physical Chemistry Chemical Physics 2011 - vol. 13(Issue 2) pp:NaN460-460
Publication Date(Web):2010/10/29
DOI:10.1039/C0CP00256A
The selective catalytic reduction (SCR) of NO by NH3 over V2O5-based catalysts is used worldwide to control NOx emission. Understanding the mechanisms involved is vital for the rational design of more effective catalysts. Here, we have performed a systematic density functional theory (DFT) study of a SCR reaction by using cluster models. Three possible mechanisms have been considered, namely (i) a Lewis acid mechanism, (ii) a Brønsted acid mechanism and (iii) a nitrite mechanism. Our calculations down-play the significance of mechanism (i) due to its high barrier as well as the incorrect reaction order. On the other hand, our calculations demonstrate that both mechanisms (ii) and (iii) can lead to a first order reaction with respect to NO with the predicted barriers being consistent with the experimental observations. Thus, we conclude: there exists two competitive pathways for SCR. Mechanism (ii) is dominant when the Brønsted acidity of the catalysts is relatively strong, while mechanism (iii) becomes important when Brønsted acidity is weak or absent. Importantly, we demonstrate that the latter two mechanisms share a common feature where N–N bond formation is ahead of N–H bond cleavage, in contrast to that in mechanism (i). Such a sequence provides an effective way to reduce the side reaction of ammonia combustion since the relatively strong N–N bond has already been formed.
Co-reporter:Xiao-Lian Jing, Qing-Chuan Chen, Chong He, Xue-Quan Zhu, Wei-Zheng Weng, Wen-Sheng Xia and Hui-Lin Wan
Physical Chemistry Chemical Physics 2012 - vol. 14(Issue 19) pp:NaN6904-6904
Publication Date(Web):2012/03/20
DOI:10.1039/C2CP40086C
The photo-induced formation of peroxide ions on the surface of cubic Ln2O3 (Ln = Nd, Sm, Gd) was studied by in situ microprobe Raman spectroscopy using a 325 nm laser as excitation source. It was found that the Raman bands of peroxide ions at 833–843 cm−1 began to grow at the expense of the Ln3+–O2− bands at 333–359 cm−1 when the Ln2O3 samples under O2 were continuously irradiated with a focused 325 nm laser beam at temperatures between 25–150 °C. The intensity of the peroxide Raman band was found to increase with increasing O2 partial pressure, whereas no peroxide band was detected on the Ln2O3 under N2 as well as on the samples first irradiated with laser under Ar or N2 followed by exposure to O2 in the dark. The experiments using 18O as a tracer further confirmed that the peroxide ions are generated by a photo-induced reaction between O2 and the lattice oxygen (O2−) species in Ln2O3. Under the excitation of 325 nm UV light, the transformation of O2 to peroxide ions on the surface of the above lanthanide sesquioxides can even take place at room temperature. Basicity of the lattice oxygen species on Ln2O3 also has an impact on the peroxide formation. Higher temperature or laser irradiation power is required to initiate the reaction between O2 and O2− species of weaker basicity.
Co-reporter:Miao Sun, Jizhe Zhang, Qinghong Zhang, Ye Wang and Huilin Wan
Chemical Communications 2009(Issue 34) pp:NaN5176-5176
Publication Date(Web):2009/07/21
DOI:10.1039/B910317A
A Keggin-type polyoxometalate (Cs1.5H1.5PW12O40)-supported Pd catalyst is efficient for the direct synthesis of H2O2 from H2 and O2 in the absence of any acid or halide additives under atmospheric pressure.
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