Organic-inorganic multifunctional hybrid catalyst giving catalytic synergies in cooperative coupling between CO₂ and propylene oxide to propylene carbonate

Kim, Daeho,Na, Kyungsu Elsevier 2018 Journal of CO₂ utilization Vol.27 No.-

<P><B>Abstract</B></P> <P>An organic-inorganic hybrid catalyst was synthesized by silylation of silanol (SiOH) groups with ammonium bromide group on the mesopore wall of mesoporous zeolite having a hierarchically nanoporous architecture, conferring both electrophilic and nucleophilic functions due to the acid sites of the zeolite and bromide in the functional group, respectively. In the coupling of carbon dioxide and propylene oxide for production of propylene carbonate, the hybrid catalyst exhibited a synergistic enhancement in activity leading to a two-fold higher product yield than the catalysts having a single catalytic function. Comprehensive reaction studies revealed that the catalytic synergy could only be obtained by achieving close proximity between the ammonium bromide group and acid sites on the zeolite surface. The acidity was also crucial, where no synergy was observed for a similarly designed organic-inorganic hybrid catalyst constructed on weakly acidic ordered mesoporous silica SBA-15. Comparison of the activation energy of the catalysts supported the observation that the zeolite-based hybrid catalyst with stronger acidity gave rise to a lower activation energy (37.3 kJ mol<SUP>−1</SUP>) than the SBA-15-based hybrid catalyst with weaker acidity (51.3 kJ mol<SUP>−1</SUP>). The mesoporous zeolite-based hybrid catalyst was very active under neat conditions without additional organic solvent, and showed good recyclability without significant loss of the initial activity for up to five runs.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Organic-inorganic hybrid catalyst is constructed on mesoporous zeolite having strong acidity. </LI> <LI> Hybrid catalyst gave catalytic synergy in coupling of CO<SUB>2</SUB> and propylene oxide to propylene carbonate. </LI> <LI> Bromide acts is the main catalyst as nucleophile for ring-opening of epoxide. </LI> <LI> Strong acid sites of zeolite are the co-catalyst as electrophile for activation of oxygen in epoxide. </LI> <LI> Close proximity between bromide and strong acidity on the zeolite surface is crucial for synergy. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Selective methane chlorination to methyl chloride by zeolite Y-based catalysts

Joo, Hyeonho,Kim, Daeho,Lim, Kwang Soo,Choi, Yong Nam,Na, Kyungsu Elsevier 2018 SOLID STATE SCIENCES Vol.77 No.-

<P><B>Abstract</B></P> <P>The CH<SUB>4</SUB> chlorination over Y zeolites was investigated to produce CH<SUB>3</SUB>Cl in a high yield. Three different catalytic systems based on Y zeolite were tested for enhancement of CH<SUB>4</SUB> conversion and CH<SUB>3</SUB>Cl selectivity: (i) HY zeolites in H<SUP>+</SUP>-form having various Si/Al ratios, (ii) Pt/HY zeolites supporting Pt metal nanoparticles, (iii) Pt/NaY zeolites in Na<SUP>+</SUP>-form supporting Pt metal nanoparticles. The reaction was carried out using the gas mixture of CH<SUB>4</SUB> and Cl<SUB>2</SUB> with the respective flow rates of 15 and 10 mL min<SUP>−1</SUP> at 300–350 °C using a fixed-bed reactor under a continuous gas flow condition (gas hourly space velocity = 3000 mL g<SUP>−1</SUP> h<SUP>−1</SUP>). Above the reaction temperature of 300 °C, the CH<SUB>4</SUB> chlorination is spontaneous even in the absence of catalyst, achieving 23.6% of CH<SUB>4</SUB> conversion with 73.4% of CH<SUB>3</SUB>Cl selectivity. Under sufficient supplement of thermal energy, Cl<SUB>2</SUB> molecules can be dissociated to two chlorine radicals, which triggered the C-H bond activation of CH<SUB>4</SUB> molecule and thereby various chlorinated methane products (i.e., CH<SUB>3</SUB>Cl, CH<SUB>2</SUB>Cl<SUB>2</SUB>, CHCl<SUB>3</SUB>, CCl<SUB>4</SUB>) could be produced. When the catalysts were used under the same reaction condition, enhancement in the CH<SUB>4</SUB> conversion was observed. The Pt-free HY zeolite series with varied Si/Al ratios gave around 27% of CH<SUB>4</SUB> conversion, but there was a slight decrease in CH<SUB>3</SUB>Cl selectivity with about 64%. Despite the difference in acidity of HY zeolites having different Si/Al ratios, no prominent effect of the Si/Al ratios on the catalytic performance was observed. This suggests that the catalytic contribution of HY zeolites under the present reaction condition is not strong enough to overcome the spontaneous CH<SUB>4</SUB> chlorination. When the Pt/HY zeolite catalysts were used, the CH<SUB>4</SUB> conversion reached further up to 30% but the CH<SUB>3</SUB>Cl selectivity decreased to 60%. Such an enhancement of CH<SUB>4</SUB> conversion could be attributed to the strong catalytic activity of HY and Pt/HY zeolite catalysts. However, both catalysts induced the radical cleavage of Cl<SUB>2</SUB> more favorably, which ultimately decreased the CH<SUB>3</SUB>Cl selectivity. Such trade-off relationship between CH<SUB>4</SUB> conversion and CH<SUB>3</SUB>Cl selectivity can be slightly broken by using Pt/NaY zeolite catalyst that is known to possess Frustrated Lewis Pairs (FLP) that are very useful for ionic cleavage of H<SUB>2</SUB> to H<SUP>+</SUP> and H<SUP>−</SUP>. Similarly, in the present work, Pt/NaY(FLP) catalysts enhanced the CH<SUB>4</SUB> conversion while keeping the CH<SUB>3</SUB>Cl selectivity as compared to the Pt/HY zeolite catalysts.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Selective chlorination of CH<SUB>4</SUB> with Cl<SUB>2</SUB> molecule was studied using zeolite Y-based catalysts. </LI> <LI> CH<SUB>4</SUB> conversion increased with HY zeolites having acidity, but CH<SUB>3</SUB>Cl selectivity decreased. </LI> <LI> CH<SUB>4</SUB> conversion increased further with Pt/HY zeolites, but CH<SUB>3</SUB>Cl selectivity decreased further. </LI> <LI> Pt/NaY with Frustrated Lewis Pairs improved CH<SUB>4</SUB> conversion and CH<SUB>3</SUB>Cl selectivity simultaneously. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

NOx and N₂O emissions over a Urea-SCR system containing both V₂O₅-WO₃/TiO₂ and Cu-zeolite catalysts in a diesel engine

Jung, Yongjin,Shin, Young Jin,Pyo, Young Dug,Cho, Chong Pyo,Jang, Jinyoung,Kim, Gangchul Elsevier 2017 CHEMICAL ENGINEERING JOURNAL -LAUSANNE- Vol.326 No.-

<P><B>Abstract</B></P> <P>To develop a novel selective catalytic reduction (SCR) system, V<SUB>2</SUB>O<SUB>5</SUB>-WO<SUB>3</SUB>/TiO<SUB>2</SUB> and Cu-zeolite catalysts were combined within one canister with the former upstream and the latter downstream. The nitrogen oxides (NOx) and N<SUB>2</SUB>O emissions for the combined catalyst were investigated under operating conditions of engine loads and speeds in a 3.4L diesel engine. The results from the combined catalyst were compared with those from the vanadium-based and Cu-zeolite catalysts alone. The NO conversion efficiencies for all the catalysts were higher than approximately 80% at temperatures ranging from 200 to 410°C, which corresponds to the NO<SUB>2</SUB> excess range. In other words, the NO<SUB>2</SUB>/NOx ratio was higher than 50% for the temperature range between 200 and 410°C, although the maximum NO<SUB>2</SUB>/NOx ratio was obtained at 270°C. Beyond 410°C, the efficiency of the Cu-zeolite catalyst remained high; however, the vanadium-based catalyst started to deteriorate at 410°C. The deterioration of the combined catalyst was not much larger than that of the vanadium-based catalyst owing to the superior capability of the Cu-zeolite catalyst. For the NO<SUB>2</SUB> conversion efficiency, the combined catalyst mostly followed the Cu-zeolite catalyst. The vanadium-based catalyst exhibited an efficiency drop at approximately 270°C, which is the temperature of the highest NO<SUB>2</SUB>/NOx ratio; however, this efficiency drop was avoided in the combined catalyst. For N<SUB>2</SUB>O produced over the catalysts, the Cu-zeolite catalyst produced the most N<SUB>2</SUB>O, while the vanadium-based catalyst produced the least. Because the amount of N<SUB>2</SUB>O produced behind the SCR was at most five times that in front of the SCR, efforts to inhibit N<SUB>2</SUB>O production from SCR are required when considering the global warming potential of N<SUB>2</SUB>O. The combined catalyst produced intermediate levels of N<SUB>2</SUB>O.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The combined vanadium-based and Cu-zeolite catalysts were configured. </LI> <LI> NO and NO<SUB>2</SUB> conversion efficiencies were investigated in a diesel engine. </LI> <LI> N<SUB>2</SUB>O produced over catalysts was inversely related to the conversion efficiency. </LI> <LI> The combined SCR system could be employed as a compromise. </LI> </UL> </P>

RuO₂ supported NaY zeolite catalysts: Effect of preparation methods on catalytic performance during aerobic oxidation of benzyl alcohol

Jung, D.,Lee, S.,Na, K. ELSEVIER 2017 SOLID STATE SCIENCES Vol.72 No.-

The effects of preparation method for RuO<SUB>2</SUB> supported zeolite catalysts on the catalytic consequences during the aerobic oxidation of benzyl alcohol to benzaldehyde were investigated. Three preparation methods, i.e., (i) simultaneous crystallization of the zeolite framework in the presence of RuCl<SUB>3</SUB> (Ru(SC)/NaY), (ii) post ion-exchange with RuCl<SUB>3</SUB> on the zeolite framework (Ru(IE)/NaY), and (iii) post support of preformed Ru metal nanoparticles on the zeolite surface (Ru(PS)/NaY), were used to construct three different RuO<SUB>2</SUB> supported NaY zeolite catalysts. The catalyst performance was investigated as functions of the reaction time and temperature, in correlation with the structural changes of the catalysts, as analyzed by X-ray diffraction (XRD). The results revealed that the catalytic consequences were dramatically affected by the preparation methods. Although similar conversion was achieved with all three catalysts, the turnover frequency (TOF) differed. The Ru(PS)/NaY catalyst exhibited the highest TOF (33-48 h<SUP>-1</SUP>), whereas the other catalysts produced much lower TOFs (9-12 h<SUP>-1</SUP>). The Ru(PS)/NaY catalyst also had the highest activation energy (E<SUB>a</SUB>) of 48.39 kJ mol<SUP>-1</SUP>, whereas the Ru(SC)/NaY and Ru(IE)/NaY catalysts had E<SUB>a</SUB> values of 18.58 and 24.11 kJ mol<SUP>-1</SUP>, respectively. Notably, the Ru(PS)/NaY catalyst yielded a significantly higher pre-exponential factor of 5.22 x 10<SUP>5</SUP> h<SUP>-1</SUP>, which is about 5 orders of magnitude larger than that of the Ru(SC)/NaY catalyst (7.15 x 10<SUP>0</SUP> h<SUP>-1</SUP>). This suggests that collision between benzyl alcohol and molecular oxygen was very intensive on the Ru(PS)/NaY catalyst, which explains the higher TOF of the Ru(PS)/NaY catalyst relative to the others in spite of the higher E<SUB>a</SUB> value of the former. In terms of recyclability, the pristine crystallinity of the zeolite framework was maintained in the Ru(SC)/NaY catalyst and the RuO<SUB>2</SUB> phase exhibited an insignificant loss of the initial activity up to three catalytic cycles, whereas Ru(PS)/NaY showed slight loss of activity and Ru(IE)/NaY showed a significant loss of activity due to the disappearance of the RuO<SUB>2</SUB> phase.

Rational synthesis of silylated Beta zeolites and selective ring opening of 1-methylnaphthalene over the NiW-supported catalysts

Lee, Su-Un,Lee, You-Jin,Kim, Jeong-Rang,Jeong, Soon-Yong Elsevier 2017 Applied Catalysis B Vol.219 No.-

<P><B>Abstract</B></P> <P>Heavy oil has been by-produced from refinery and petrochemical processes, and its use as low-value fuels has been restricted by stricter environmental regulations due to heavy molecules, multi-ring aromatics, and high sulfur content. In a bi-functional catalyst system of metal and zeolitic acid, balancing metallic (from metal element) and acidic function (from zeolite elements) is essential for harnessing the selective ring opening (SRO) reaction with the aim of upgrading the heavy oil. Here, we report a synthetic strategy to control the acid site distribution of Beta zeolite through the silylation reaction with tetramethyl orthosilicate (TMOS), tetraethyl orthosilicate (TEOS), and tetrabutyl orthosilicate (TBOS) as silylation agents. As the size of alkyl chain group in the silylation agents gets larger, the silylation agents were suppressed to spread into the channels and thus the formation of SiO<SUB>2</SUB> layer was intentionally occurred on the external surface of the zeolite. Resulting from the selectively deposited SiO<SUB>2</SUB> layer, NiW metals supported on each silylated Beta zeolite altered the metal distribution and further the balance of metallic and acidic function. NiW catalyst supported on TBOS-silylated Beta zeolite exhibited the best catalytic performance toward the SRO reaction of 1-methylnaphthalene in a fix-bed reaction system, proving the optimal balance of metallic and acidic functions. We expect that this study will benefit the control over the selective silylation reaction in order to optimize the balance of metallic and acidic functions in the bi-functional catalysts, and, hence, to promote properly aromatic saturation (hydrogenation) and ring opening (hydrocracking) for selective ring opening products.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The distribution of acid sites in zeolites was modified by silylation with various alkyl chains. </LI> <LI> Large silylation agents induce to deposit SiO<SUB>2</SUB> on the external surface of zeolites. </LI> <LI> NiW/silylated zeolite alters the balance of metallic and acidic functions. </LI> <LI> Selective ring opening of 1-methylnaphthalene by NiW/silylated zeolite was tested. </LI> <LI> The optimal balance of bi-functional catalysts improve conversion and selectivity. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

1P-360 Synthesis of decyl glucoside from D-glucose with 1-decanol by direct glucosidation over solid acid catalysts and its estrogenicity

정상민,이원준,정경환,이헌,정상철 한국공업화학회 2017 한국공업화학회 연구논문 초록집 Vol.2017 No.1

Synthesis of decyl glucoside was asserted over various zeolite catalysts by direct glucosidation of D-glucose. The estrogenicity of decyl glucoside was evaluated to confirm the possibility as an alternative surfactant of nonyl phenol. Catalytic properties of the microporous zeolite in the preparation of decyl glucoside from D-glucose with 1-decanol by single-step direct glucosidation. The zeolite catalysts were consisted of different acidic properties and pore topologies. The effect of acidities and pore topologies of the zeolite catalysts were discussed considering to the conversion and yields to the glucosidation. The estrogenicity of decyl glucopyranoside was estimated using E-assay method to compare that of nonylphenol. The high conversions were obtained inversely to the order of acid strength of the zeolite catalysts. The decyl glucopyranoside represented apparently lower estrogenic cell proliferation compared with nonylphenol.

Preparation of decyl glucoside from D-glucose with 1-decanol on microporous zeolite catalysts and evaluation of estrogenicity

이원준,이헌,정경환,정상철 한국공업화학회 2018 한국공업화학회 연구논문 초록집 Vol.2018 No.0

Preparation of decyl glucoside D-glucose with 1-decanol was studied on various zeolite catalysts by direct glucosidation. The estrogenicity of decyl glucoside was evaluated to confirm the possibility as an alternative surfactant of nonyl phenol. Catalytic properties of the microporous zeolite in the preparation of decyl glucoside from D-glucose with 1-decanol by single-step direct glucosidation. The zeolite catalysts were consisted of different acidic properties and pore topologies. The effect of acidities and pore topologies of the zeolite catalysts were discussed considering to the conversion and yields to the glucosidation. The estrogenicity of decyl glucopyranoside was estimated using E-assay method to compare that of nonylphenol. The high conversions were obtained inversely to the order of acid strength of the zeolite catalysts. The decyl glucopyranoside represented apparently lower estrogenic cell proliferation compared with nonylphenol.

Nitrate reduction on surface of Pd/Sn catalysts supported by coal fly ash-derived zeolites

Park, Jaehyeong,Hwang, Yuhoon,Bae, Sungjun Elsevier 2019 Journal of hazardous materials Vol.374 No.-

<P><B>Abstract</B></P> <P>In this study, we synthesized four zeolites (i.e., Zeolite-X&A9, -X&A&HS12, -X&HS15, -X&HS18) from coal fly ash (CFA), and evaluated their potential for use as support materials to fabricate novel Pd-Sn bimetallic catalysts for reactive and selective reduction of NO<SUB>3</SUB> <SUP>−</SUP> to N<SUB>2</SUB>. The successive transformation of zeolite (Na-A and Na-X to hydroxy sodalite (HS)) was observed with increasing crystallization time from 9 to 18 h, which resulted in different degrees of crystallinity, morphology, BET surface area, and pore volume. Compared to other monometallic and bimetallic catalysts, Pd-Sn/Zeolite-X&HS15 (crystallization time = 15 h) showed remarkable nitrate removal (100%) with the highest kinetic rate constant (<I>k</I> = 0.055 min<SUP>−1</SUP>, K’ = 0.219 min<SUP>−1</SUP> g<SUB>cat</SUB> <SUP>−1</SUP>, K’’ = 2.922 L min<SUP>−1</SUP> g<SUB>Pd</SUB> <SUP>−1</SUP>) and N<SUB>2</SUB> selectivity (88.1%). These results can be attributed to high surface area and stability of each of the zeolite phases (i.e., Na-X and HS). The reaction mechanism was elucidated by Energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy analyses, demonstrating the presence of Pd°, Sn°, and Sn<SUP>2+</SUP> and the uniform distribution of proximate Pd-Sn ensembles on the surface. These results suggest new promising strategies for applying industrial solid waste-derived zeolites to the synthesis of novel bimetallic catalysts to ensure efficient and economical denitrification of wastewater.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Four different zeolites were synthesized from coal fly ash (CFA). </LI> <LI> Novel Pd-Sn catalysts supported by zeolite showed selective reduction of NO<SUB>3</SUB> <SUP>−</SUP> to N<SUB>2</SUB>. </LI> <LI> Change in zeolite phase from X & A to HS was observed as increasing crystallization time. </LI> <LI> Pd-Sn/Zeolite-X&HS15 showed the highest rate constant and N<SUB>2</SUB> selectivity. </LI> <LI> Increase in content of HS with high surface area led to enhanced reduction of NO<SUB>3</SUB> <SUP>−</SUP> to N<SUB>2</SUB>. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Effects of Ce and Nb additives on the de-NOx performance of SCR/CDPF system based on Cu-beta zeolite for diesel vehicles

Zhao, Yingying,Choi, Byungchul,Kim, Daeseok Elsevier 2017 Chemical engineering science Vol.164 No.-

<P><B>Abstract</B></P> <P>In this study, the de-NOx performance of the Cu-beta zeolite (BEA) selective catalytic reduction (SCR) catalyst with Ce and Nb as additives was investigated for the diesel catalytic reduction catalyzed diesel particulate filter (SCR/CDPF) system. The Cu-BEA catalyst with the Ce and Nb additives improved the NOx conversion, compared to the Cu-BEA catalyst without additives, under conditions of both standard and fast SCR reaction. This result is related to the strength of the intensity ratio as (Cu2p3 B peak)/(Cu2p3 A peak) for the Ce and Nb added catalysts. At the aging temperature of >650°C, the Cu-BEA-Nb catalyst showed better de-NOx performance than the other catalysts, because the Nb<SUB>2</SUB>O<SUB>5</SUB> (Nb<SUP>5+</SUP>) of the aged Cu-BEA-Nb catalyst remained. The Cu-BEA-CeNb catalyst was most affected by HC, and the addition of Nb to the Cu-BEA catalyst improved the oxidation ability and inhibited the HC poison at a high temperature.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Ce and Nb additives improved the NOx conversion of pristine Cu-BEA. </LI> <LI> Addition of Nb to Cu-BEA improved oxidation ability and inhibited HC poisoning. </LI> <LI> Cu-BEA-Nb was the most promising catalyst for application in diesel SCR/CDPF. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Electrochemical Behavior of Pt-Ru Catalysts on Zeolite-templated Carbon Supports for Direct Methanol Fuel Cells

Tae-Jin Lim,이슬이,유윤종,박수진 대한화학회 2014 Bulletin of the Korean Chemical Society Vol.35 No.12

Zeolite-templated carbons (ZTCs), which have high specific surface area, were prepared by a conventional templating method using microporous zeolite-Y for catalyst supports in direct methanol fuel cells. The ZTCs were synthesized at different temperatures to investigate the characteristics of the surface produced and their electrochemical properties. Thereafter, Pt-Ru was deposited at different carbonization temperatures by a chemical reduction method. The crystalline and structural features were investigated using X-ray diffraction and scanning electron microscopy. The textural properties of the ZTCs were investigated by analyzing N2/77 K adsorption isotherms using the Brunauer-Emmett-Teller equation, while the micro- and meso-pore size distributions were analyzed using the Barrett-Joyner-Halenda and Harvarth-Kawazoe methods, respectively. The surface morphology was characterized using transmission electron microscopy and inductively coupled plasma-mass spectrometry. The electrochemical properties of the Pt-Ru/ZTCs catalysts were also analyzed by cyclic voltammetry measurements. From the results, the ZTCs carbonized at 900 °C show the highest specific surface areas. In addition, ZTC900-PR led to uniform dispersion of Pt-Ru on the ZTCs, which enhanced the electro-catalytic activity of the Pt-Ru catalysts. The particle size of ZTC900-PR catalyst is about 3.4 nm, also peak current density from the CV plot is 12.5 mA/cm2. Therefore, electro-catalytic activity of the ZTC900-PR catalyst is higher than those of ZTC1000-PR catalyst.