Chinese Journal of Catalysis

Table of Contents for VOL.37 No.12

2016, 37 (12): 0-0.

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Adsorption/reaction energetics measured by microcalorimetry and correlated with reactivity on supported catalysts: A review

Lin Li, Jian Lin, Xiaoyu Li, Aiqin Wang, Xiaodong Wang, Tao Zhang

2016, 37 (12): 2039-2052. DOI: 10.1016/S1872-2067(16)62578-0

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The formations and transformations of the chemical bonds of reactants and intermediates on catalyst surfaces occur in conjunction with the evolution of heat during catalytic reactions. Measurement of this evolved heat is helpful in terms of understanding the nature of the interactions between the catalyst and the adsorbed species, and provides insights into the reactivity of the catalyst. Although various techniques have previously been applied to assessments of evolved heat, direct measurements using a Tian-Calvet microcalorimeter are currently the most reliable method for this purpose. In this review, we summarize the relationship between the adsorption/reaction energetics determined by microcalorimetry and the reactivities of supported catalysts, and examine the important role of microcalorimetry in understanding catalytic performance from the energetic point of view.

Selective reduction of carbon dioxide to carbon monoxide over Au/CeO₂ catalyst and identification of reaction intermediate

Xiaobing Zhu, Xin Qu, Xiaosong Li, Jinglin Liu, Jianhao Liu, Bin Zhu, Chuan Shi

2016, 37 (12): 2053-2058. DOI: 10.1016/S1872-2067(16)62538-X

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CO₂ selective reduction to CO with H₂ over a CeO₂-supported nano-Au catalyst at atmospheric pressure was investigated. A high CO₂ conversion, approaching the thermodynamic equilibrium value, and nearly 100% CO selectivity were obtained. The surface formate intermediates generated during the reverse water-gas shift reaction at 400℃ were identified using in situ diffuse-reflectance infrared Fourier-transform spectroscopy. The formate consumption to give CO and H₂O, determined using mass spectrometry, indicated that the reaction proceeded via an associative formate mechanism; this contributes to the high Au/CeO₂ catalytic activity at low temperatures.

Time-resolved photoluminescence of anatase/rutile TiO₂ phase junction revealing charge separation dynamics

Xiuli Wang, Shuai Shen, Zhaochi Feng, Can Li

2016, 37 (12): 2059-2068. DOI: 10.1016/S1872-2067(16)62574-3

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Junctions are an important structure that allows charge separation in solar cells and photocatalysts. Here, we studied the charge transfer at an anatase/rutile TiO₂ phase junction using time-resolved photoluminescence spectroscopy. Visible (~500 nm) and near-infrared (NIR,~830 nm) emissions were monitored to give insight into the photoinduced charges of anatase and rutile in the junction, respectively. New fast photoluminescence decay components appeared in the visible emission of rutile-phase dominated TiO₂ and in the NIR emission of many mixed phase TiO₂ samples. The fast decays confirmed that the charge separation occurred at the phase junction. The visible emission intensity from the mixed phase TiO₂ increased, revealing that charge transfer from rutile to anatase was the main pathway. The charge separation slowed the microsecond time scale photoluminescence decay rate for charge carriers in both anatase and rutile. However, the millisecond decay of the charge carriers in anatase TiO₂ was accelerated, while there was almost no change in the charge carrier dynamics of rutile TiO₂. Thus, charge separation at the anatase/rutile phase junction caused an increase in the charge carrier concentration on a microsecond time scale, because of slower electron-hole recombination. The enhanced photocatalytic activity previously observed at anatase/rutile phase junctions is likely caused by the improved charge carrier dynamics we report here. These findings may contribute to the development of improved photocatalytic materials.

Fe-Beta zeolite for selective catalytic reduction of NO_x with NH₃: Influence of Fe content

Yan Xia, Wangcheng Zhan, Yun Guo, Yanglong Guo, Guanzhong Lu

2016, 37 (12): 2069-2078. DOI: 10.1016/S1872-2067(16)62534-2

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Fe doped Beta zeolite with different Fe contents were prepared by ion exchange by changing the volume or the concentration of a Fe salt solution. For a particular mass of Fe salt precursor, the concentration of the metal salt solution during ion exchange influenced the ion exchange capacity of Fe, and resulted in different activities of the Fe-Beta catalyst. Fe-Beta catalysts with the Fe contents of (2.6, 6.3 and 9) wt% were synthesized using different amounts of 0.02 mol/L Fe salt solution. These catalysts were studied by various characterization techniques and their NH₃-SCR activities were evaluated. The Fe-Beta catalyst with the Fe content of 6.3 wt% exhibited the highest activity, with a temperature range of 202-616℃ where the NO_x conversion was > 80%. The Fe content in Beta zeolite did not influence the structure of Beta zeolite and valence state of Fe. Compared with the Fe-Beta catalysts with low Fe content (2.6 wt%), Fe-Beta catalysts with 6.3 wt% Fe content possessed more isolated Fe³⁺ active sites which led to its higher NH₃-SCR activity. A high capacity for NH₃ and NO adsorption, and a high activity for NO oxidation also contributed to the high NH₃-SCR activity of the Fe-Beta catalyst with 6.3 wt%. However, when the Fe content was further increased to 9.0 wt%, the amount of Fe_xO_y nanoparticles increased while the amount of isolated Fe³⁺ active sites was unchanged, which promoted NH₃ oxidation and decreased the NH₃-SCR activity at high temperature.

Electro-polymerization fabrication of PANI@GF electrode and its energy-effective electrocatalytic performance in electro-Fenton process

Jinli Yu, Tianfu Liu, Haiyue Liu, Yi Wang

2016, 37 (12): 2079-2085. DOI: 10.1016/S1872-2067(16)62525-1

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An energy-effective polyaniline coated graphite felt (PANI@GF) composite cathode for the elec-tro-Fenton (E-Fenton) process was synthesized through an electro-polymerization method. The electrocatalytic activity of the cathode for the 2e-ORR process was investigated and dimethyl phthalate (DMP) was used as a model substrate to evaluate its performance in the E-Fenton process. The as-prepared PANI@GF composite possessed a three-dimensional porous structure, which is favorable for O₂ diffusion, while the large amount of N atoms in the conductive polyaniline (PANI) enhanced 2e-ORR reactivity. The DMP degradation of the E-Fenton system using PANI@GF was significantly enhanced owing to the improvement in ORR performance. The apparent kinetic constant for DMP degradation was 0.0753 min^-1, five times larger than that of GF. The optimal carbonization temperature and polymerization time for the preparation of the PANI@GF composite cathode was found to be 900℃ and 1 h, respectively. Measurement conditions are a crucial factor for proper evaluation of cathode electrocatalytic performance. Accordingly, the O₂ flow rate, Fe²⁺ concentration, and pH for DMP degradation were optimized at 0.4 L/min, 1.0 mmol/L, and 3.0, respectively. These results indicate that the present PANI@GF composite cathode is energy-effective and promising for potential use as an E-Fenton system cathode for the removal of organic pollutants in wastewater.

Efficient oxidation of cinnamon oil to natural benzaldehyde over β-cyclodextrin-functionalized MWCNTs

Zujin Yang, Xia Zhang, Yanxiong Fang, Zebao Rui, Hongbing Ji

2016, 37 (12): 2086-2097. DOI: 10.1016/S1872-2067(16)62543-3

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We have designed and prepared β-cyclodextrin (β-CD)-functionalized multi-walled nanotubes (MWCNTs-g-CD) for the oxidation of cinnamon oil to natural benzaldehyde under aqueous conditions. The synergistic effect of combining MWCNTs with β-CD led to a remarkable increase in the performance of the MWCNTs-g-CD for the catalytic oxidation of cinnamaldehyde, which exhibited 95% cinnamaldehyde conversion and 85% selectivity to natural benzaldehyde with a short reaction time of 10 min. The MWCNTs-g-CD also exhibited outstanding recyclability with good stability, showing no discernible decrease in their catalytic activity over five reaction cycles.

Ultra-deep oxidative desulfurization of fuel with H₂O₂ catalyzed by phosphomolybdic acid supported on silica

Yongsheng Tian, Guanghui Wang, Juan Long, Jiawei Cui, Wei Jin, Danlin Zeng

2016, 37 (12): 2098-2105. DOI: 10.1016/S1872-2067(16)62558-5

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A highly active catalyst of phosphomolybdic acid (HPMo) was prepared and applied in the catalytic oxidative desulfurization (CODS) system. The catalyst was characterized by FT-IR, XRD, XPS and superconducting NMR. The influences of m(catalyst)/m(oil), V(H₂O₂)/V(oil), reaction temperature and reaction time on the fractional conversion of benzothiophene (BT) and dibenzothiophene (DBT) were investigated. GC-MS and micro-coulometric methods were employed to investigate the reaction. The catalyst has high desulfurization activity in the removal of BT and DBT under mild conditions. The recycling experiments indicated that DBT and BT removal could still reach 95.2% and 95.7% after 10 cycles.

Fe₃O₄@UiO-66-NH₂ core-shell nanohybrid as stable heterogeneous catalyst for Knoevenagel condensation

Yanmei Zhang, Tianlin Dai, Fan Zhang, Jing Zhang, Gang Chu, Chunshan Quan

2016, 37 (12): 2106-2113. DOI: 10.1016/S1872-2067(16)62562-7

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Magnetic separation is an attractive alternative to filtration or centrifugation for separating solid catalysts from a liquid phase. Here, core-shell Fe₃O₄@UiO-66-NH₂ nanohybrids with well-defined structures were constructed by dispersing magnets in a dimethylformamide (DMF) solution containing two metal-organic framework (MOF) precursors, namely ZrCl₄ and 2-aminobenzenetricarboxylic acid. This method is simpler and more efficient than previously reported step-by-step method in which magnets were consecutively dispersed in DMF solutions each containing one MOF precursor, and the obtained Fe₃O₄@UiO-66-NH₂ with three assembly cycles has a higher degree of crystallinity and porosity. The core-shell Fe₃O₄@UiO-66-NH₂ is highly active and selective in Knoevenagel condensations because of the bifunctionality of UiO-66-NH₂ and better mass transfer in the nano-sized shells. It also has good recycling stability, and can be recovered magnetically and reused at least four times without significant loss of catalytic activity and framework integrity. The effects of substitution on the reactivity of benzaldehyde and of substrate size were also investigated.

Proton-gradient-transfer acid complexes and their catalytic performance for the synthesis of geranyl acetate

Yongle Chen, Shiya Ding, Wentao Zheng, Yiyang Zhang, Youting Wu, Xingbang Hu

2016, 37 (12): 2114-2121. DOI: 10.1016/S1872-2067(16)62577-9

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Special proton-gradient-transfer acid complexes (PGTACs) in which the bonded protons are not equivalent and have gradients in transfer ability, acidity, and reactivity were reported. The acidity gradient of the protons gave the PGTACs excellent catalytic activity and selectivity in the esterification of terpenols. These PGTACs are "reaction-induced self-separation catalysts" and can be easily reused. The kinetics with PGTACs as catalyst in the esterification of geraniol were also studied for use in engineering design.

Morphology effect of zirconia support on the catalytic performance of supported Ni catalysts for dry reforming of methane

Weizuo Li, Zhongkui Zhao, Yanhua Jiao, Guiru Wang

2016, 37 (12): 2122-2133. DOI: 10.1016/S1872-2067(16)62540-8

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An immature pinecone shaped hierarchically structured zirconia (ZrO₂-ipch) and a cobblestone-like zirconia nanoparticulate (ZrO₂-cs), both with the monoclinic phase (m-phase), were synthesized by the facile hydrothermal method and used as the support for a Ni catalyst for the dry reforming of methane (DRM) with CO₂. ZrO₂-ipch is a much better support than ZrO₂-cs and the traditional ZrO₂ irregular particles made by a simple precipitation method (ZrO₂-ip). The supported Ni catalyst on ZrO₂-ipch (Ni/ZrO₂-ipch) exhibited outstanding catalytic activity and coke-resistant stability compared to the ones on ZrO₂-cs (Ni/ZrO₂-cs) and ZrO₂-ip (Ni/ZrO₂-ip). Ni/ZrO₂-ip exhibited the worst catalytic performance. The origin of the significantly enhanced catalytic performance was revealed by characterization including XRD, N2 adsorption measurement (BET), TEM, H₂-TPR, CO chemisorption, CO₂-TPD, XPS and TGA. The superior catalytic activity of Ni/ZrO₂-ipch to Ni/ZrO₂-cs or Ni/ZrO₂-ip was ascribed to a higher Ni dispersion, increased reducibility, enhanced oxygen mobility, and more basic sites with a higher strength, which were due to the unique hierarchically structural morphology of the ZrO₂-ipch support. Ni/ZrO₂-ipch exhibited better stability for the DRM reaction than Ni/ZrO₂-ip, which was ascribed to its higher resistance to Ni sintering due to a strengthened metal-support interaction and the confinement effect of the mesopores and coke deposition resistance. The higher coking resistance of Ni/ZrO₂-ipch for the DRM reaction in comparison with Ni/ZrO₂-ip orignated from the coke-removalability of the higher amount of lattice oxygen and more basic sites, confirmed by XPS and CO₂-TPD analysis, and the stabilized Ni on the Ni/ZrO₂-ipch catalyst by the confinement effect of the mesopores of the hierarchical ZrO₂-ipch support. The superior catalytic performance and coking resistance of the Ni/ZrO₂-ipch catalyst makes it a promising candidate for synthesis gas production from the DRM reaction.

Alkylation of toluene with tert-butyl alcohol over HPW-modified Hβ zeolite

Yuanyuan Wang, Hua Song, Xinglong Sun

2016, 37 (12): 2134-2141. DOI: 10.1016/S1872-2067(16)62587-1

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An Hβ-supported heteropoly acid (H₃PW₁₂O₄₀ (HPW)/Hβ) catalyst was successfully prepared by wetness impregnation, and investigated in the alkylation of toluene with tert-butyl alcohol for the synthesis of 4-tert-butyltoluene (PTBT). X-ray diffraction, scanning electron microscopy, transmission electron microscopy, fourier-transform infrared spectroscopy, inductively coupled plasma-optical emission spectrometry, the brunauer emmett teller (BET) method, temperature-programmed NH₃ desorption, and pyridine adsorption infrared spectroscopy were used to characterize the catalyst. The results showed that loading HPW on Hβ effectively increased the B acidity and decreased the pore size of Hβ. The B acidity of HPW/Hβ was 142.97 μmol/g, which is 69.74% higher than that of Hβ (84.23 μmol/g). The catalytic activity of the HPW/Hβ catalyst was much better than that of the parent Hβ zeolite because of its high B acidity. The toluene conversion over HPW/Hβ reached 73.1%, which is much higher than that achieved with Hβ (54.0%). When HPW was loaded on Hβ, the BET surface area of Hβ decreased from 492.5 to 379.6 m²/g, accompanied by a significant decrease in the pore size from 3.90 to 3.17 nm. Shape selectivity can therefore play an important role and increase the product selectivity of the HPW/Hβ catalyst compared with that of the parent Hβ. PTBT (kinetic diameter 0.58 nm) can easily diffuse through the narrowed pores of HPW/Hβ, but 3-tert-butyltoluene (kinetic diameter 0.65 nm) diffusion is restricted because of steric hindrance in these narrow pores. This results in high PTBT selectivity over HPW/Hβ (around 81%). The HPW/Hβ catalyst gave a stable catalytic performance in reusability tests.

Contents for Volume 37 (2016)

2016, 37 (12): 2142-2167.

Abstract ( 189 ) [Full Text(HTML)] ()

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Author Index for Volume 37 (2016)

2016, 37 (12): 2168-2178.

Abstract ( 104 ) [Full Text(HTML)] ()

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