Yun Hin Taufiq Yap | UPM - Universiti Putra Malaysia (original) (raw)
Papers by Yun Hin Taufiq Yap
Fuel, 2015
Biodiesel is a clean-burning alternative fuel but it is susceptible to lower calorific value due ... more Biodiesel is a clean-burning alternative fuel but it is susceptible to lower calorific value due to autoxidation in the presence of oxygen, which hinders its widespread use. Organic germanium Ge-132 is a prospective solution to this problem. It is expected that Ge-132 may affect the energy content of blending biodiesel. This paper presents an experimental investigation of the effect of Ge-132 addition to palm biodiesel on physicochemical properties. Three concentrations including 5ppm, 8ppm and 10ppm added to BD20 to study their fuel physical characteristics effect. The fuel and additive was blend by using ultrasonic emulsifier for 2 minutes before experiment. The results show that BD20 with additive Ge-132 produced 0.48%-1.07% higher density and 0.7%-1.7% higher kinematic viscosity and 0.09%-0.6% higher calorific value compared to BD20 without the additive. The higher calorific value blending biodiesel attribute by the carbon content on Ge-132. Compared to BD20, the blended biodiesel with additive Ge-132 produce higher density, kinematic viscosity and calorific value which attribute the increase the performance and better fuel consumption.
A 3 wt% La-promoted Ni/Al2O3 catalyst was prepared via wet co-impregnation technique and physicoc... more A 3 wt% La-promoted Ni/Al2O3 catalyst was prepared via wet co-impregnation technique and physicochemically-characterized. Lanthanum was responsible for better metal dispersion; hence higher BET specific surface area (96.0 m2 g−1) as compared to the unpromoted Ni/Al2O3 catalyst (85.0 m2 g−1). In addition, the La-promoted catalyst possessed finer crystallite size (9.1 nm) whilst the unpromoted catalyst measured 12.8 nm. Subsequently, glycerol dry reforming was performed at atmospheric pressure and temperatures ranging from 923 to 1123 K employing CO2-to-glycerol ratio from zero to five. Significantly, the reaction results have yielded syngas as main gaseous products with H2:CO ratios always below than 2.0 with concomitant maximum 96% glycerol conversion obtained at the CO2-toglycerol ratio of 1.67. In addition, the glycerol consumption rate can be adequately captured using power law modelling with the order of reactions equal 0.72 and 0.14 with respect to glycerol and CO2 whilst the activation energy was 35.0 kJ mol−1. A 72 h longevity run moreover revealed that the catalyst gave a stable catalytic performance.
Fuel, 2015
Empty fruit bunches (EFBs) from the palm plantation sector are abundant agricultural waste produc... more Empty fruit bunches (EFBs) from the palm plantation sector are abundant agricultural waste products in Malaysia. Supercritical water gasification (SCWG) is a prominent way to convert high-moisture-content biomass such as EFBs into valuable end products. This investigation is focused on EFB conversion into hydrogen-rich products using SCWG (temperature = 380 °C and pressure ≈ 240 bar). Lignocellulosic model compounds (xylan, cellulose, and lignin) were used to study the degradation patterns and gas compositions under similar reaction conditions. The effect of the EFB/water ratio and the SCWG reaction time on the composition of the product gas was examined. Carbon gasification does not improve with increasing EFB/water ratio as well as with increasing reaction time caused by the thermally stable tar formation during reaction. The hydrogen concentration was found to be increased with reaction time along with raising the EFB/water ratio to 0.3 g (3.75 wt%). In addition, the possibility of using palm oil mill effluent as a reaction medium in comparison to deionized water was analyzed.
Journal of Catalysis, 2000
The interaction of n-butane with a ((VO)2P2O7) catalyst has been investigated by temperature-prog... more The interaction of n-butane with a ((VO)2P2O7) catalyst has been investigated by temperature-programmed desorption and anaerobic temperature-programmed reaction. n-Butane has been shown to adsorb on the (VO)2P2O7 to as a butyl-hydroxyl pair. When adsorption is carried out at 223 K, upon temperature programming some of the butylhydroxyl species recombine resulting in butane desorption at 260 K. However, when adsorption is carried out at 423 K, the hydroxyl species of the butyl-hydroxyl pair migrate away from the butyl species during the adsorption, forming water which is detected in the gas phase. Butane therefore is not observed to desorb at 260 K after we lowered the temperature to 223 K under the butane/helium from the adsorption temperature of 423 K prior to temperature programming from that temperature to 1100 K under a helium stream. Anaerobic temperature-programmed oxidation of n-butane produces butene and butadiene at a peak maximum temperature of 1000 K; this is exactly the temperature at which, upon temperature programming, oxygen evolves from the lattice and desorbs as O2. This, and the fact that the amount of oxygen desorbing from the (VO)2P2O7 at 1000 K is the same as that required for the oxidation of the n-butane to butene and butadiene, strongly suggests (i) that lattice oxygen as it emerges at the surface is the selective oxidant and (ii) that its appearance at the surface is the rate-determining step in the selective oxidation of n-butane. The surface of the (VO)2P2O7 catalyst on which this selective oxidation takes place has had approximately two monolayers of oxygen removed from it by unselective oxidation of the n-butane to CO, CO2, and H2O between 550 and 950 K and has had approximately one monolayer of carbon deposited on it at 1000 K. It is apparent, therefore, that the original crystallography of the (VO)2P2O7 catalyst will not exist during this selective oxidation and that theories that relate selectivity in partial oxidation to the (100) face of the (VO)2P2O7 catalyst cannot apply in this case.
Journal of Biomedical Nanotechnology, 2014
Intercalation of Zn/Al layered double hydroxide (LDH) with benzophenone 9 (B9), a strong ultravio... more Intercalation of Zn/Al layered double hydroxide (LDH) with benzophenone 9 (B9), a strong ultraviolet (UV) absorber, had been carried out by two different routes; co-precipitation and ion exchange method. Powder X-ray diffraction (PXRD) patterns of co-precipitated (ZB9C) and ion exchanged product (ZB9I) showed basal spacing of 15.9 Å and 16.6 Å, respectively, as a result of the intercalation of B9 anions into the lamellae spaces of LDH. Intercalation was further confirmed by Fourier transform infrared spectra (FTIR), carbon, hydrogen, nitrogen and sulfur (CHNS) and thermogravimetric and differential thermogravimetric (TGA/DTG) studies. UV-vis absorption properties of the nanocomposite was investigated with diffuse reflectance UV-visible spectrometer and showed broader UV absorption range. Furthermore, stability of sunscreen molecules in LDH interlayer space was tested in deionized water, artificial sea water and skin pH condition to show slow deintercalation and high retention in host. Cytotoxicity study of the synthesized nanocomposites on human dermal fibroblast (HDF) cells shows no significant cytotoxicity after 24 h exposure for test concentrations up to 25 g/mL.
Comptes Rendus Chimie, 2009
Catalysis Letters, 2010
VOHPO 4•0.5H 2O synthesized via the alcohol reduction of VOPO 4•2H 2O was mechanochemical treated... more VOHPO 4•0.5H 2O synthesized via the alcohol reduction of VOPO 4•2H 2O was mechanochemical treated for 30 min in three different media, i.e. cyclohexane, ethanol and air. XRD results revealed that their structure became less crystalline compared to the unmilled material. SEM showed that the particles for the milled materials become smaller and unique features were observed in the different type of media used. The reactivity of the oxygen species linked to V 5+ and V 4+ were also affected by the milling process. The selectivity to maleic anhydride from n-butane oxidation were observed to increase in line with the increase in the oxygen species associated with V 5+ and the presence of isolated V 5+ phase. A correlation was observed between the crystallite size of the pyrophosphate phase at (020) plane with the maleic anhydride selectivity.
Applied Catalysis A: General, 2013
Applied Catalysis A: General, 2012
Trimethylolpropane (TMP) esters are potential biodegradable basestock for biolubricant. In order ... more Trimethylolpropane (TMP) esters are potential biodegradable basestock for biolubricant. In order to attain environmental benignity, attention has been focused on utilizing heterogeneous catalysts for production of TMP esters. Alkaline homogeneous catalysts tend to react with free fatty acids to produce unwanted soap, thus reducing the overall product yield. This study had focused on the synthesis of calcium methoxide and investigating its potential as heterogeneous catalyst for the transesterification of TMP and palm oil methyl esters (POME) to TMP esters. The performance of synthesized calcium methoxide as a catalyst was examined by characterizing it through some instrumental techniques. X-ray diffraction (XRD) showed calcium methoxide has been successfully synthesized. Scanning electron microscopy (SEM) displayed thermally resistant surface structure with good porosity; BET showed high surface area; particle size analysis evidenced reasonable size of catalyst particles; and thermogravimetry (TGA) revealed good thermal stability of synthesized calcium methoxide. Moreover, the catalyst was found to possess mesoporous surface by pore size analysis through Barrett-Joyner-Halenda (BJH) method. The results of transesterification reaction indicated satisfactory catalytic activity of synthesized calcium methoxide and the TMP triesters yield obtained was 80.35% after 2 h, 87.48% after 4 h, 91.30% after 6 h and 92.38% after 8 h reaction time.
Catalysis Letters, 2009
The nature and the role of oxygen species and vanadium oxidation states on the activation of n-bu... more The nature and the role of oxygen species and vanadium oxidation states on the activation of n-butane for selective oxidation to maleic anhydride were investigated. Bi-Fe doped and undoped vanadium phosphate catalysts were used a model catalyst. XRD revealed that Bi-Fe mixture dopants led to formation of αII-VOPO4 phase together with (VO)2P2O7 as a dominant phase when the materials were heated in n-butane/air to form the final catalysts. TPR analysis showed that the reduction behaviour of Bi-Fe doped catalysts was dominated by the reduction peak assigned to the reduction of V5+ species as compared to the undoped catalyst, which gave the reduction of V4+ as the major feature. An excess of the oxygen species (O2−) associated with V5+ in Bi-Fe doped catalysts improved the maleic anhydride selectivity but significantly lowering the rate of n-butane conversion. The reactive pairing of V4+-O− was shown to be the centre for n-butane activation. It is proposed that the availability and appearance of active oxygen species (O−) on the surface of vanadium phosphate catalyst is the rate determining step of the overall reaction.
Renewable and Sustainable Energy Reviews, 2015
Catalysis Letters, 2007
The present work addresses the influence of microwave irradiation on undoped and doped vanadium p... more The present work addresses the influence of microwave irradiation on undoped and doped vanadium phosphate catalysts. These catalysts were prepared via VOPO4 · 2H2O. The catalyst’s precursors‚ VOHPO4 · 0.5H2O were subjected to microwave irradiation and comparison was made with the conventional heating. The interaction of these complex materials with microwave and the addition of several doponts (Nb, Bi, Co, Mo) provide interesting improvements in catalyst preparation found to be a faster, develop higher surface area, higher activity and selectivity for the oxidation of n-butane to maleic anhydride. All the catalysts were characterized by using a combination of powder XRD, H2-TPR, BET surface area and SEM.
Catalysis Today, 2004
Bi 2 O 3 catalysts have been prepared via precipitation method by using Bi(NO 3 ) 3 ·5H 2 O as a ... more Bi 2 O 3 catalysts have been prepared via precipitation method by using Bi(NO 3 ) 3 ·5H 2 O as a starting material and NaOH as the precipitating agent. The influence of bismuth concentration on the formation of Bi 2 O 3 nanocrystals was investigated by using XRD, BET, FTIR, SEM ...
Journal of Catalysis, 2000
The interaction of n-butane with a ((VO) 2 P 2 O 7 ) catalyst has been investigated by temperatur... more The interaction of n-butane with a ((VO) 2 P 2 O 7 ) catalyst has been investigated by temperature-programmed desorption and anaerobic temperature-programmed reaction. n-Butane has been shown to adsorb on the (VO) 2 P 2 O 7 to as a butyl-hydroxyl pair. When adsorption is carried out at 223 K, upon temperature programming some of the butyl-hydroxyl species recombine resulting in butane desorption at 260 K. However, when adsorption is carried out at 423 K, the hydroxyl species of the butyl-hydroxyl pair migrate away from the butyl species during the adsorption, forming water which is detected in the gas phase. Butane therefore is not observed to desorb at 260 K after we lowered the temperature to 223 K under the butane/helium from the adsorption temperature of 423 K prior to temperature programming from that temperature to 1100 K under a helium stream. Anaerobic temperature-programmed oxidation of n-butane produces butene and butadiene at a peak maximum temperature of 1000 K; this is exactly the temperature at which, upon temperature programming, oxygen evolves from the lattice and desorbs as O 2 . This, and the fact that the amount of oxygen desorbing from the (VO) 2 P 2 O 7 at ∼1000 K is the same as that required for the oxidation of the n-butane to butene and butadiene, strongly suggests (i) that lattice oxygen as it emerges at the surface is the selective oxidant and (ii) that its appearance at the surface is the rate-determining step in the selective oxidation of n-butane. The surface of the (VO) 2 P 2 O 7 catalyst on which this selective oxidation takes place has had approximately two monolayers of oxygen removed from it by unselective oxidation of the n-butane to CO, CO 2 , and H 2 O between 550 and 950 K and has had approximately one monolayer of carbon deposited on it at ∼1000 K. It is apparent, therefore, that the original crystallography of the (VO) 2 P 2 O 7 catalyst will not exist during this selective oxidation and that theories that relate selectivity in partial oxidation to the (100) face of the (VO) 2 P 2 O 7 catalyst cannot apply in this case.
Electrochemical and Solid State Letters, 2004
Reaction Kinetics and Catalysis Letters, 2003
Co-promoted vanadyl pyrophosphate catalyst (Co/V = 2.23 %) was prepared by classical organic meth... more Co-promoted vanadyl pyrophosphate catalyst (Co/V = 2.23 %) was prepared by classical organic method via VOHPO4.0.5H2O precursor and calcined for 100 h in a mixture of n-butane in air. The synthesised catalyst was characterised by N2 physisorption, ICP, X-ray diffraction, scanning electron microscopy, and temperature-programmed desorption of oxygen.
Catalysis Letters, 2006
Two vanadium phosphate catalysts (VPH1 and VPH2) prepared via hydrothermal method are described a... more Two vanadium phosphate catalysts (VPH1 and VPH2) prepared via hydrothermal method are described and discussed. Both catalysts exhibited only highly crystalline pyrophosphate phase. SEM showed that the morphologies of these catalysts are in plate-like shape and not in the normal rosette-type clusters. Temperature-programmed reduction in H2 resulted two reduction peaks at high temperature in the range of 600–1100 K. The second reduction peak appeared at 1074 K occurred as a sharp peak indicated that the oxygen species originated from V4+ phase are having difficulty to be removed and their nature are less reactive compared to other methods of preparation. Modified VPH2 gave better catalytic performance for n-butane oxidation to maleic anhydride contributed by a higher BET surface area, high mobility and reactivity of the lattice oxygen associated to the V4+ which involved in the hydrocarbon’s activation. A slight increased of the V5+ phase also enhanced the activity of the VPH2 catalyst.
Journal of Natural Gas Chemistry, 2006
Industrial & Engineering Chemistry Research, 2010
The vanadyl hydrogen phosphate hemihydrate (VOHPO 4 · 0.5H 2 O), with well-defined crystal size, ... more The vanadyl hydrogen phosphate hemihydrate (VOHPO 4 · 0.5H 2 O), with well-defined crystal size, has been successfully synthesized for the first time, using a simple one-step solvothermal process that was free of surfactants and water and had a short reaction time and low temperature. The synthesis was performed via the reaction of V 2 O 5 and H 3 PO 4 with an aliphatic alcohol (1-propanol or 1-butanol) at high temperatures (373, 393, and 423 K) in a high-pressure autoclave. The mixture of reactions directly gave the VOHPO 4 · 0.5H 2 O, which is a valuable commercial catalyst precursor for the selective oxidation of n-butane to maleic anhydride. The catalyst precursors were dried by microwave irradiation. The reaction conditions (by varying the reducing agent and reaction temperature) were used further for optimization of the crystallite size, surface area, morphology, and activity of the nanostructure of vanadium phosphate oxide [(VO) 2 P 2 O 7 ] catalyst. This new method significantly reduced the preparation time and lowered the production temperature (50%) of catalyst precursor (VOHPO 4 · 0.5H 2 O), when compared to conventional hydrothermal synthesis methods. The as-prepared (VO) 2 P 2 O 7 catalyst under various conditions exhibited remarkably different physical and chemical properties, indicating the potential of the suggested method in tuning the crystalline structure and surface area of (VO) 2 P 2 O 7 to improve its catalytic performance. It was found that the length of the carbon chain in an alcohol and reaction temperature in the solvothermal condition had a great impact on the chemical and physical properties of resulting catalysts. Interestingly, there was no trace of VO(H 2 PO 4 ) 2 , which is an impurity noted to be readily formed under solvothermal preparation conditions. The precursors and catalysts were characterized using a combination of powder X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) surface area measurement, scanning electron microscopy (SEM), and temperature-programmed reduction in hydrogen (H 2 -TPR). A correlation between the surface area of the catalyst and the activity was observed. Finally, the yield of maleic anhydride was significantly increased from 21% for conventional catalyst to 38% for the new solvothermal catalyst.
Journal of Porous Materials, 2001
Oil palm trunk is a major lignocellulosic-rich, solid waste material generated from palm-oil upst... more Oil palm trunk is a major lignocellulosic-rich, solid waste material generated from palm-oil upstream industry. The activated carbons prepared from oil palm trunk pretreated with phosphoric acid with the ratio of the acid to the precursor of 0.9, followed by carbonization and activation by carbon dioxide resulted in a high surface area of more than 1800 m2/g with 90% content of micropore surface area. The surface area and the nature of the porosity of the resulting activated carbons were found to be dependent on the amount of the activator used for a fixed quantity of the precursor. Pretreatment of the precursor at low ratio of the phosphoric acid has added advantage, due to the tremendous increase in the apparent surface area of the resulting activated carbon and at the same time enriching its micropore nature. This could result in the conservation of the micropore fraction. On the other hand, using too high a ratio of the phosphoric acid to the precursor did not increase the apparent surface area very much, but instead destroyed the micropore component, and thus increasing the mesopore fraction of the resulting activated carbon. This study also shows that oil palm trunk, a by-product of oil palm industry has a great potential as a raw material for activated carbon production.
Fuel, 2015
Biodiesel is a clean-burning alternative fuel but it is susceptible to lower calorific value due ... more Biodiesel is a clean-burning alternative fuel but it is susceptible to lower calorific value due to autoxidation in the presence of oxygen, which hinders its widespread use. Organic germanium Ge-132 is a prospective solution to this problem. It is expected that Ge-132 may affect the energy content of blending biodiesel. This paper presents an experimental investigation of the effect of Ge-132 addition to palm biodiesel on physicochemical properties. Three concentrations including 5ppm, 8ppm and 10ppm added to BD20 to study their fuel physical characteristics effect. The fuel and additive was blend by using ultrasonic emulsifier for 2 minutes before experiment. The results show that BD20 with additive Ge-132 produced 0.48%-1.07% higher density and 0.7%-1.7% higher kinematic viscosity and 0.09%-0.6% higher calorific value compared to BD20 without the additive. The higher calorific value blending biodiesel attribute by the carbon content on Ge-132. Compared to BD20, the blended biodiesel with additive Ge-132 produce higher density, kinematic viscosity and calorific value which attribute the increase the performance and better fuel consumption.
A 3 wt% La-promoted Ni/Al2O3 catalyst was prepared via wet co-impregnation technique and physicoc... more A 3 wt% La-promoted Ni/Al2O3 catalyst was prepared via wet co-impregnation technique and physicochemically-characterized. Lanthanum was responsible for better metal dispersion; hence higher BET specific surface area (96.0 m2 g−1) as compared to the unpromoted Ni/Al2O3 catalyst (85.0 m2 g−1). In addition, the La-promoted catalyst possessed finer crystallite size (9.1 nm) whilst the unpromoted catalyst measured 12.8 nm. Subsequently, glycerol dry reforming was performed at atmospheric pressure and temperatures ranging from 923 to 1123 K employing CO2-to-glycerol ratio from zero to five. Significantly, the reaction results have yielded syngas as main gaseous products with H2:CO ratios always below than 2.0 with concomitant maximum 96% glycerol conversion obtained at the CO2-toglycerol ratio of 1.67. In addition, the glycerol consumption rate can be adequately captured using power law modelling with the order of reactions equal 0.72 and 0.14 with respect to glycerol and CO2 whilst the activation energy was 35.0 kJ mol−1. A 72 h longevity run moreover revealed that the catalyst gave a stable catalytic performance.
Fuel, 2015
Empty fruit bunches (EFBs) from the palm plantation sector are abundant agricultural waste produc... more Empty fruit bunches (EFBs) from the palm plantation sector are abundant agricultural waste products in Malaysia. Supercritical water gasification (SCWG) is a prominent way to convert high-moisture-content biomass such as EFBs into valuable end products. This investigation is focused on EFB conversion into hydrogen-rich products using SCWG (temperature = 380 °C and pressure ≈ 240 bar). Lignocellulosic model compounds (xylan, cellulose, and lignin) were used to study the degradation patterns and gas compositions under similar reaction conditions. The effect of the EFB/water ratio and the SCWG reaction time on the composition of the product gas was examined. Carbon gasification does not improve with increasing EFB/water ratio as well as with increasing reaction time caused by the thermally stable tar formation during reaction. The hydrogen concentration was found to be increased with reaction time along with raising the EFB/water ratio to 0.3 g (3.75 wt%). In addition, the possibility of using palm oil mill effluent as a reaction medium in comparison to deionized water was analyzed.
Journal of Catalysis, 2000
The interaction of n-butane with a ((VO)2P2O7) catalyst has been investigated by temperature-prog... more The interaction of n-butane with a ((VO)2P2O7) catalyst has been investigated by temperature-programmed desorption and anaerobic temperature-programmed reaction. n-Butane has been shown to adsorb on the (VO)2P2O7 to as a butyl-hydroxyl pair. When adsorption is carried out at 223 K, upon temperature programming some of the butylhydroxyl species recombine resulting in butane desorption at 260 K. However, when adsorption is carried out at 423 K, the hydroxyl species of the butyl-hydroxyl pair migrate away from the butyl species during the adsorption, forming water which is detected in the gas phase. Butane therefore is not observed to desorb at 260 K after we lowered the temperature to 223 K under the butane/helium from the adsorption temperature of 423 K prior to temperature programming from that temperature to 1100 K under a helium stream. Anaerobic temperature-programmed oxidation of n-butane produces butene and butadiene at a peak maximum temperature of 1000 K; this is exactly the temperature at which, upon temperature programming, oxygen evolves from the lattice and desorbs as O2. This, and the fact that the amount of oxygen desorbing from the (VO)2P2O7 at 1000 K is the same as that required for the oxidation of the n-butane to butene and butadiene, strongly suggests (i) that lattice oxygen as it emerges at the surface is the selective oxidant and (ii) that its appearance at the surface is the rate-determining step in the selective oxidation of n-butane. The surface of the (VO)2P2O7 catalyst on which this selective oxidation takes place has had approximately two monolayers of oxygen removed from it by unselective oxidation of the n-butane to CO, CO2, and H2O between 550 and 950 K and has had approximately one monolayer of carbon deposited on it at 1000 K. It is apparent, therefore, that the original crystallography of the (VO)2P2O7 catalyst will not exist during this selective oxidation and that theories that relate selectivity in partial oxidation to the (100) face of the (VO)2P2O7 catalyst cannot apply in this case.
Journal of Biomedical Nanotechnology, 2014
Intercalation of Zn/Al layered double hydroxide (LDH) with benzophenone 9 (B9), a strong ultravio... more Intercalation of Zn/Al layered double hydroxide (LDH) with benzophenone 9 (B9), a strong ultraviolet (UV) absorber, had been carried out by two different routes; co-precipitation and ion exchange method. Powder X-ray diffraction (PXRD) patterns of co-precipitated (ZB9C) and ion exchanged product (ZB9I) showed basal spacing of 15.9 Å and 16.6 Å, respectively, as a result of the intercalation of B9 anions into the lamellae spaces of LDH. Intercalation was further confirmed by Fourier transform infrared spectra (FTIR), carbon, hydrogen, nitrogen and sulfur (CHNS) and thermogravimetric and differential thermogravimetric (TGA/DTG) studies. UV-vis absorption properties of the nanocomposite was investigated with diffuse reflectance UV-visible spectrometer and showed broader UV absorption range. Furthermore, stability of sunscreen molecules in LDH interlayer space was tested in deionized water, artificial sea water and skin pH condition to show slow deintercalation and high retention in host. Cytotoxicity study of the synthesized nanocomposites on human dermal fibroblast (HDF) cells shows no significant cytotoxicity after 24 h exposure for test concentrations up to 25 g/mL.
Comptes Rendus Chimie, 2009
Catalysis Letters, 2010
VOHPO 4•0.5H 2O synthesized via the alcohol reduction of VOPO 4•2H 2O was mechanochemical treated... more VOHPO 4•0.5H 2O synthesized via the alcohol reduction of VOPO 4•2H 2O was mechanochemical treated for 30 min in three different media, i.e. cyclohexane, ethanol and air. XRD results revealed that their structure became less crystalline compared to the unmilled material. SEM showed that the particles for the milled materials become smaller and unique features were observed in the different type of media used. The reactivity of the oxygen species linked to V 5+ and V 4+ were also affected by the milling process. The selectivity to maleic anhydride from n-butane oxidation were observed to increase in line with the increase in the oxygen species associated with V 5+ and the presence of isolated V 5+ phase. A correlation was observed between the crystallite size of the pyrophosphate phase at (020) plane with the maleic anhydride selectivity.
Applied Catalysis A: General, 2013
Applied Catalysis A: General, 2012
Trimethylolpropane (TMP) esters are potential biodegradable basestock for biolubricant. In order ... more Trimethylolpropane (TMP) esters are potential biodegradable basestock for biolubricant. In order to attain environmental benignity, attention has been focused on utilizing heterogeneous catalysts for production of TMP esters. Alkaline homogeneous catalysts tend to react with free fatty acids to produce unwanted soap, thus reducing the overall product yield. This study had focused on the synthesis of calcium methoxide and investigating its potential as heterogeneous catalyst for the transesterification of TMP and palm oil methyl esters (POME) to TMP esters. The performance of synthesized calcium methoxide as a catalyst was examined by characterizing it through some instrumental techniques. X-ray diffraction (XRD) showed calcium methoxide has been successfully synthesized. Scanning electron microscopy (SEM) displayed thermally resistant surface structure with good porosity; BET showed high surface area; particle size analysis evidenced reasonable size of catalyst particles; and thermogravimetry (TGA) revealed good thermal stability of synthesized calcium methoxide. Moreover, the catalyst was found to possess mesoporous surface by pore size analysis through Barrett-Joyner-Halenda (BJH) method. The results of transesterification reaction indicated satisfactory catalytic activity of synthesized calcium methoxide and the TMP triesters yield obtained was 80.35% after 2 h, 87.48% after 4 h, 91.30% after 6 h and 92.38% after 8 h reaction time.
Catalysis Letters, 2009
The nature and the role of oxygen species and vanadium oxidation states on the activation of n-bu... more The nature and the role of oxygen species and vanadium oxidation states on the activation of n-butane for selective oxidation to maleic anhydride were investigated. Bi-Fe doped and undoped vanadium phosphate catalysts were used a model catalyst. XRD revealed that Bi-Fe mixture dopants led to formation of αII-VOPO4 phase together with (VO)2P2O7 as a dominant phase when the materials were heated in n-butane/air to form the final catalysts. TPR analysis showed that the reduction behaviour of Bi-Fe doped catalysts was dominated by the reduction peak assigned to the reduction of V5+ species as compared to the undoped catalyst, which gave the reduction of V4+ as the major feature. An excess of the oxygen species (O2−) associated with V5+ in Bi-Fe doped catalysts improved the maleic anhydride selectivity but significantly lowering the rate of n-butane conversion. The reactive pairing of V4+-O− was shown to be the centre for n-butane activation. It is proposed that the availability and appearance of active oxygen species (O−) on the surface of vanadium phosphate catalyst is the rate determining step of the overall reaction.
Renewable and Sustainable Energy Reviews, 2015
Catalysis Letters, 2007
The present work addresses the influence of microwave irradiation on undoped and doped vanadium p... more The present work addresses the influence of microwave irradiation on undoped and doped vanadium phosphate catalysts. These catalysts were prepared via VOPO4 · 2H2O. The catalyst’s precursors‚ VOHPO4 · 0.5H2O were subjected to microwave irradiation and comparison was made with the conventional heating. The interaction of these complex materials with microwave and the addition of several doponts (Nb, Bi, Co, Mo) provide interesting improvements in catalyst preparation found to be a faster, develop higher surface area, higher activity and selectivity for the oxidation of n-butane to maleic anhydride. All the catalysts were characterized by using a combination of powder XRD, H2-TPR, BET surface area and SEM.
Catalysis Today, 2004
Bi 2 O 3 catalysts have been prepared via precipitation method by using Bi(NO 3 ) 3 ·5H 2 O as a ... more Bi 2 O 3 catalysts have been prepared via precipitation method by using Bi(NO 3 ) 3 ·5H 2 O as a starting material and NaOH as the precipitating agent. The influence of bismuth concentration on the formation of Bi 2 O 3 nanocrystals was investigated by using XRD, BET, FTIR, SEM ...
Journal of Catalysis, 2000
The interaction of n-butane with a ((VO) 2 P 2 O 7 ) catalyst has been investigated by temperatur... more The interaction of n-butane with a ((VO) 2 P 2 O 7 ) catalyst has been investigated by temperature-programmed desorption and anaerobic temperature-programmed reaction. n-Butane has been shown to adsorb on the (VO) 2 P 2 O 7 to as a butyl-hydroxyl pair. When adsorption is carried out at 223 K, upon temperature programming some of the butyl-hydroxyl species recombine resulting in butane desorption at 260 K. However, when adsorption is carried out at 423 K, the hydroxyl species of the butyl-hydroxyl pair migrate away from the butyl species during the adsorption, forming water which is detected in the gas phase. Butane therefore is not observed to desorb at 260 K after we lowered the temperature to 223 K under the butane/helium from the adsorption temperature of 423 K prior to temperature programming from that temperature to 1100 K under a helium stream. Anaerobic temperature-programmed oxidation of n-butane produces butene and butadiene at a peak maximum temperature of 1000 K; this is exactly the temperature at which, upon temperature programming, oxygen evolves from the lattice and desorbs as O 2 . This, and the fact that the amount of oxygen desorbing from the (VO) 2 P 2 O 7 at ∼1000 K is the same as that required for the oxidation of the n-butane to butene and butadiene, strongly suggests (i) that lattice oxygen as it emerges at the surface is the selective oxidant and (ii) that its appearance at the surface is the rate-determining step in the selective oxidation of n-butane. The surface of the (VO) 2 P 2 O 7 catalyst on which this selective oxidation takes place has had approximately two monolayers of oxygen removed from it by unselective oxidation of the n-butane to CO, CO 2 , and H 2 O between 550 and 950 K and has had approximately one monolayer of carbon deposited on it at ∼1000 K. It is apparent, therefore, that the original crystallography of the (VO) 2 P 2 O 7 catalyst will not exist during this selective oxidation and that theories that relate selectivity in partial oxidation to the (100) face of the (VO) 2 P 2 O 7 catalyst cannot apply in this case.
Electrochemical and Solid State Letters, 2004
Reaction Kinetics and Catalysis Letters, 2003
Co-promoted vanadyl pyrophosphate catalyst (Co/V = 2.23 %) was prepared by classical organic meth... more Co-promoted vanadyl pyrophosphate catalyst (Co/V = 2.23 %) was prepared by classical organic method via VOHPO4.0.5H2O precursor and calcined for 100 h in a mixture of n-butane in air. The synthesised catalyst was characterised by N2 physisorption, ICP, X-ray diffraction, scanning electron microscopy, and temperature-programmed desorption of oxygen.
Catalysis Letters, 2006
Two vanadium phosphate catalysts (VPH1 and VPH2) prepared via hydrothermal method are described a... more Two vanadium phosphate catalysts (VPH1 and VPH2) prepared via hydrothermal method are described and discussed. Both catalysts exhibited only highly crystalline pyrophosphate phase. SEM showed that the morphologies of these catalysts are in plate-like shape and not in the normal rosette-type clusters. Temperature-programmed reduction in H2 resulted two reduction peaks at high temperature in the range of 600–1100 K. The second reduction peak appeared at 1074 K occurred as a sharp peak indicated that the oxygen species originated from V4+ phase are having difficulty to be removed and their nature are less reactive compared to other methods of preparation. Modified VPH2 gave better catalytic performance for n-butane oxidation to maleic anhydride contributed by a higher BET surface area, high mobility and reactivity of the lattice oxygen associated to the V4+ which involved in the hydrocarbon’s activation. A slight increased of the V5+ phase also enhanced the activity of the VPH2 catalyst.
Journal of Natural Gas Chemistry, 2006
Industrial & Engineering Chemistry Research, 2010
The vanadyl hydrogen phosphate hemihydrate (VOHPO 4 · 0.5H 2 O), with well-defined crystal size, ... more The vanadyl hydrogen phosphate hemihydrate (VOHPO 4 · 0.5H 2 O), with well-defined crystal size, has been successfully synthesized for the first time, using a simple one-step solvothermal process that was free of surfactants and water and had a short reaction time and low temperature. The synthesis was performed via the reaction of V 2 O 5 and H 3 PO 4 with an aliphatic alcohol (1-propanol or 1-butanol) at high temperatures (373, 393, and 423 K) in a high-pressure autoclave. The mixture of reactions directly gave the VOHPO 4 · 0.5H 2 O, which is a valuable commercial catalyst precursor for the selective oxidation of n-butane to maleic anhydride. The catalyst precursors were dried by microwave irradiation. The reaction conditions (by varying the reducing agent and reaction temperature) were used further for optimization of the crystallite size, surface area, morphology, and activity of the nanostructure of vanadium phosphate oxide [(VO) 2 P 2 O 7 ] catalyst. This new method significantly reduced the preparation time and lowered the production temperature (50%) of catalyst precursor (VOHPO 4 · 0.5H 2 O), when compared to conventional hydrothermal synthesis methods. The as-prepared (VO) 2 P 2 O 7 catalyst under various conditions exhibited remarkably different physical and chemical properties, indicating the potential of the suggested method in tuning the crystalline structure and surface area of (VO) 2 P 2 O 7 to improve its catalytic performance. It was found that the length of the carbon chain in an alcohol and reaction temperature in the solvothermal condition had a great impact on the chemical and physical properties of resulting catalysts. Interestingly, there was no trace of VO(H 2 PO 4 ) 2 , which is an impurity noted to be readily formed under solvothermal preparation conditions. The precursors and catalysts were characterized using a combination of powder X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) surface area measurement, scanning electron microscopy (SEM), and temperature-programmed reduction in hydrogen (H 2 -TPR). A correlation between the surface area of the catalyst and the activity was observed. Finally, the yield of maleic anhydride was significantly increased from 21% for conventional catalyst to 38% for the new solvothermal catalyst.
Journal of Porous Materials, 2001
Oil palm trunk is a major lignocellulosic-rich, solid waste material generated from palm-oil upst... more Oil palm trunk is a major lignocellulosic-rich, solid waste material generated from palm-oil upstream industry. The activated carbons prepared from oil palm trunk pretreated with phosphoric acid with the ratio of the acid to the precursor of 0.9, followed by carbonization and activation by carbon dioxide resulted in a high surface area of more than 1800 m2/g with 90% content of micropore surface area. The surface area and the nature of the porosity of the resulting activated carbons were found to be dependent on the amount of the activator used for a fixed quantity of the precursor. Pretreatment of the precursor at low ratio of the phosphoric acid has added advantage, due to the tremendous increase in the apparent surface area of the resulting activated carbon and at the same time enriching its micropore nature. This could result in the conservation of the micropore fraction. On the other hand, using too high a ratio of the phosphoric acid to the precursor did not increase the apparent surface area very much, but instead destroyed the micropore component, and thus increasing the mesopore fraction of the resulting activated carbon. This study also shows that oil palm trunk, a by-product of oil palm industry has a great potential as a raw material for activated carbon production.