Investigating time-dependent Zn species over Zn-based catalysts in glycerol carbonylation with urea and their roles in the reaction mechanism

Nguyen-Phu, Huy,Shin, Eun Woo Elsevier 2018 Applied Catalysis A Vol.561 No.-

<P><B>Abstract</B></P> <P>In this work, two different Zn-based catalysts – ZnO, and ZnAl mixed oxide (ZnAlO) – were employed to investigate Zn-phase-dependent catalysis in glycerol carbonylation with urea as a function of reaction times. ZnAlO catalyst exhibited higher selectivity and yield of glycerol carbonate (GC) over a wide range of glycerol conversion than the ZnO catalyst. The time-dependent Zn species and reaction intermediates were observed in the solid and liquid phases at various reaction times through FTIR and XRD measurements in order to understand Zn-containing intermediates and corresponding reaction routes over each catalyst. The low GC selectivity in the reaction over the ZnO catalyst was closely connected to the formation of zinc glycerolate (ZnGly) in the solid phase. For the ZnO catalyst, ZnGly was formed in the solid phase even at an initial reaction time by the reaction between Zn NCO complex and glycerol, resulting in the loss of GC selectivity. Alternatively, over a ZnAlO catalyst, the formation of the Zn isocyanate (NCO) complex was dominant up to 2 h of reaction time in both the liquid and solid phases. After 2 h of reaction time, ZnGly was observed in the spent ZnAlO catalyst along with decreasing GC selectivity. The relative formation rates of Zn-containing reaction intermediates (ZnGly and Zn NCO complex) over the ZnAlO catalyst were affected by the Zn phases over the solid catalysts and the ratio of urea to glycerol in the liquid phase during the reaction time.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Reaction-time dependent Zn species over ZnO and ZnAlO catalysts was observed in glycerol carbonylation with urea. </LI> <LI> The role of these Zn species (zinc glycerolate (ZnGly) and Zn NCO complex) in the reaction routes was suggested. </LI> <LI> For ZnO catalyst, ZnGly was formed at initial time from Zn NCO complex and glycerol, resulting in low GC selectivity (52–56%). </LI> <LI> Over ZnAlO catalyst, ZnGly was produced after t = 2 h via the Zn NCO complex, decreasing GC selectivity from 92% to 78%. </LI> <LI> ZnAlO catalyst exhibited higher selectivity and yield of GC over a wide range of glycerol conversion than ZnO catalyst. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Dual catalysis over ZnAl mixed oxides in the glycerolysis of urea: Homogeneous and heterogeneous reaction routes

Nguyen-Phu, Huy,Park, Chan-yi,Shin, Eun Woo Elsevier 2018 Applied Catalysis A Vol.552 No.-

<P><B>Abstract</B></P> <P>In this work, we prepared ZnO, ZnAl<SUB>2</SUB>O<SUB>4</SUB>, and ZnAl mixed oxides with different metal molar ratios and applied them for synthesizing glycerol carbonate (GC) from glycerol and urea. The reaction routes related to the Zn species over the ZnAl mixed oxides were investigated. The ZnAl mixed oxides were found to consist of two Zn crystalline phases: ZnO and ZnAl<SUB>2</SUB>O<SUB>4</SUB>. From the reaction results, the ZnAl mixed oxides showed much higher glycerol conversion and GC yield than the ZnO and ZnAl<SUB>2</SUB>O<SUB>4</SUB>. During the reaction, the dissolution of the Zn species from the ZnO phase over the ZnAl mixed oxides was observed while the ZnAl<SUB>2</SUB>O<SUB>4</SUB> phase remained insoluble. The ZnO phase provided a homogeneous reaction route <I>via</I> the dissolved Zn species, resulting in the formation of a Zn complex containing the isocyanate (NCO) and zinc glycerolate. In contrast, the insoluble ZnAl<SUB>2</SUB>O<SUB>4</SUB> phase was responsible for not only a heterogeneous reaction route, but also adsorption of the Zn NCO complex on the catalyst. We proposed that the adsorbed Zn NCO complex could play a role as an active site for an additional heterogeneous reaction route. Therefore, the ZnAl mixed oxides exhibited high GC yields through the dual catalysis routes: the homogeneous reaction route over the ZnO phase and the heterogeneous reaction route over the ZnAl<SUB>2</SUB>O<SUB>4</SUB> phase.</P> <P><B>Highlights</B></P> <P> <UL> <LI> ZnAl mixed oxide catalysts are synthesized for the glycerolysis with urea. </LI> <LI> ZnAl mixed oxides are composed of two Zn crystalline phases: ZnO and ZnAl<SUB>2</SUB>O<SUB>4</SUB>. </LI> <LI> Zn species dissolved from ZnO involves homogeneous reaction via a Zn NCO complex. </LI> <LI> The Zn NCO complex adsorbs on ZnAl<SUB>2</SUB>O<SUB>4</SUB> and also involves heterogeneous reaction. </LI> <LI> Dual reaction routes over ZnAl mixed oxides enhance the catalytic performance. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Enhanced electrical properties of oxide semiconductor thin-film transistors with high conductivity thin layer insertion for the channel region

Nguyen, Cam Phu Thi,Raja, Jayapal,Kim, Sunbo,Jang, Kyungsoo,Le, Anh Huy Tuan,Lee, Youn-Jung,Yi, Junsin Elsevier 2017 APPLIED SURFACE SCIENCE - Vol.396 No.-

<P><B>Abstract</B></P> <P>This study examined the performance and the stability of indium tin zinc oxide (ITZO) thin film transistors (TFTs) by inserting an ultra-thin indium tin oxide (ITO) layer at the active/insulator interface. The electrical properties of the double channel device (ITO thickness of 5nm) were improved in comparison with the single channel ITZO or ITO devices. The TFT characteristics of the device with an ITO thickness of less than 5nm were degraded due to the formation of an island-like morphology and the carriers scattering at the active/insulator interface. The 5 nm-thick ITO inserted ITZO TFTs (optimal condition) exhibited a superior field effect mobility (∼95cm<SUP>2</SUP>/V·s) compared with the ITZO-only TFTs (∼34cm<SUP>2</SUP>/V·s). The best characteristics of the TFT devices with double channel layer are due to the lowest surface roughness (0.14nm) and contact angle (50.1°) that result in the highest hydrophicility, and the most effective adhesion at the surface. Furthermore, the threshold voltage shifts for the ITO/ITZO double layer device decreased to 0.80 and −2.39V compared with 6.10 and −6.79V (for the ITZO only device) under positive and negative bias stress, respectively. The falling rates of E<SUB>A</SUB> were 0.38eV/V and 0.54eV/V for the ITZO and ITO/ITZO bi-layer devices, respectively. The faster falling rate of the double channel devices suggests that the trap density, including interface trap and semiconductor bulk trap, can be decreased by the ion insertion of a very thin ITO film into the ITZO/SiO<SUB>2</SUB> reference device. These results demonstrate that the double active layer TFT can potentially be applied to the flat panel display.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The characteristics of thin film transistors using double active layers are examined. </LI> <LI> Electrical characteristics have been improved for the double active layers devices. </LI> <LI> The total trap density can be decreased by insert-ion of ultrathin ITO film. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Fabrication of ZnO nanorods for gas sensing applications using hydrothermal method.

Nguyen, Cam Phu Thi,La, Phan Phuong Ha,Trinh, Thanh Thuy,Le, Tuan Anh Huy,Bong, Sungjae,Jang, Kyungsoo,Ahn, Shihyun,Yi, Junsin American Scientific Publishers 2014 Journal of Nanoscience and Nanotechnology Vol.14 No.8

<P>We showed well-aligned zinc oxide (ZnO) nanorod arrays synthesized using hydrothermal method at atmospheric pressure. The influence of fabrication conditions such as Zn2+/hexamethylentriamin concentration ratio, and growth temperature on the formation of ZnO nanorods was investigated. Scanning Electron Microscope (SEM) images and X-ray Diffraction (XRD) analysis were used to confirm the single crystal of ZnO nanorods, which showed wurtzite structure with growth direction of [0001] (the c-axis). Photoluminescence (PL) measurements of ZnO nanorods revealed an intense ultraviolet peak at 388.5 nm (3.19 eV) at room temperature. The results showed that the ZnO seed layers had strong influence on the growth of vertically aligned ZnO nanorods. The gas sensor based on ZnO nanorod arrays had the most selectivity with n-butanol gas (within 2 surveyed gas: ethanol and n-butanol) and showed a higher sensitivity of 222, fast response time of 15 seconds, recovery time of 110 seconds and lower operating temperature of 200-250 C than the sensor based on the ZnO film in the same detecting conditions.</P>

Bias–stress-induced threshold voltage shift dependence of negative charge trapping in the amorphous indium tin zinc oxide thin-film transistors

Nguyen, Cam Phu Thi,Trinh, Thanh Thuy,Dao, Vinh Ai,Raja, Jayapal,Jang, Kyungsoo,Le, Tuan Anh Huy,Iftiquar, S M,Yi, Junsin Institute of Physics 2013 Semiconductor science and technology Vol.28 No.10

<P>Indium tin zinc oxide (ITZO)-based thin-film transistors (TFTs) were fabricated by dc magnetron sputtering in Ar + O<SUB>2</SUB> reactive gas, at room temperature. We present the effect of post-deposition annealing of ITZO thin films on the oxygen vacancies and on the characteristics of TFT devices. When the annealing temperature was increased from room temperature to 350 °C, the resistivity of ITZO film increased from 2.05 × 10<SUP>1</SUP> to 2.60 × 10<SUP>3</SUP> Ω cm and the interface trap density (<I>N</I><SUB>t</SUB>) of the TFTs reduced from 3.18 × 10<SUP>13</SUP> to 4.83 × 10<SUP>11</SUP> cm<SUP>−2</SUP>. The TFT with the ITZO film which was annealed at 350 °C showed a very small shift in turn-on voltage, even after applying positive bias stress of +12 V for 10<SUP>4</SUP> s. The current–voltage characteristics of 350 °C annealing temperature sample indicated that these TFTs were in an enhanced mode of transistor operation with a high on-to-off current ratio of ∼1.26 × 10<SUP>6</SUP>, high field-effect mobility of 14.17 cm<SUP>2</SUP> V<SUP>−1</SUP> s<SUP>−1</SUP>, and low subthreshold slope of 1.23 V/dec. The trapping time reduced from 3720 to 1546 s as the annealing temperature increased from room temperature to 350 °C. These results suggest that thermal annealing played an important role in reducing defects as well as improvement in stability of the TFTs.</P>

Glycerol carbonation with CO 2 and La 2 O 2 CO 3 /ZnO catalysts prepared by two different methods: Preferred reaction route depending on crystalline structure

Park, Chan-yi,Nguyen-Phu, Huy,Shin, Eun Woo Elsevier 2017 Molecular catalysis Vol.435 No.-

<P>La2O2CO3/ZnO catalysts for glycerol carbonation with CO2 to produce glycerol carbonate were prepared by two different methods - co-precipitation (conventional method) and ethylene glycol combustion (novel method) and investigated their catalytic properties and performance through characterization and reaction tests. La2O2CO3/ZnO prepared by the novel method (NLZ) showed higher yields of glycerol carbonate than La2O2CO3/ZnO prepared by the conventional method (CLZ) due to extremely high selectivity of glycerol carbonate by NLZ, even though NLZ exhibited lower glycerol conversions. Depending on the preparation method, predominant La2O2CO3 phases were different: monoclinic La2O2CO3 for NLZ and hexagonal La2O2CO3 for CLZ. From characterization of the spent catalysts, zinc glycerolate, an intermediate in this reaction, was formed in a large aggregate of nanoparticles over the spent CLZ, while the spent NLZ contained a trace amount of zinc glycerolate. These different catalytic behaviors were explained on the basis of catalytic reaction routes and La2O2CO3 structures. (C) 2017 Elsevier B.V. All rights reserved.</P>

메탄 습식 개질 반응용 Ni/Ce_xZr_1-xO₂-Al₂O₃ 촉매의 반응 특성: Ce_xZr_1-xO₂ 첨가에 의한 물 활성화 효과

정해원,웬푸후이,왕명연,김상윤,신은우,Haewon Jung,Huy Nguyen-Phu,Mingyan Wang,Sang Yoon Kim,Eun Woo Shin 한국화학공학회 2023 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.61 No.3

In this study, we investigated the effect of the Ce_xZr_1-xO₂ (CZ) addition onto Ni/Al₂O₃ catalysts on the catalytic performance in methane steam reforming. In the reaction results, the CZ-added Ni/Al₂O₃ catalyst showed higher CH₄ conversion and H₂ yield under the same reaction conditions than Ni/Al₂O₃. From the characterization data, the two catalysts had similar support porosity and Ni dispersion, confirming that the two properties could not determine the catalytic performance. However, the oxygen vacancy over the CZ-added Ni/Al₂O₃ catalyst induced an efficient steam activation at low reaction temperatures, resulting in an increase in the catalytic activity and H₂ yield.

폴리에틸렌 분해 반응에서 불균일 Ru 촉매의 지지체에 따른 촉매 활성 비교

김영찬(Young Chan Kim),권태은(Taeeun Kwon),김태협(Tae Hyup Kim),Huy Nguyen-Phu,노인수(Insoo Ro) 한국에너지기후변화학회 2023 한국에너지기후변화학회 학술대회 Vol.2023 No.5