Aromatization of n-Hexane over metal modified H-ZSM-5 zeolite catalysts

The aromatization of n-hexane was studied over H-ZSM-5 (SiO2/Al2O3 = 70 and %XRD crystallinity = 66%), Ga/H-ZSM-5, Zn/H-ZSM-5 and Mo/H-ZSM-5 catalysts prepared by the incipient impregnation method and calcined at 500oC. The aromatization reactions were carried out at 500oC. BET, NH3-TPD, H2-TPR and XRD techniques were used in characterization of the catalysts in a preliminary attempt to correlate structure and catalytic behaviour. The catalytic activity of H-ZSM-5 was improved when impregnated with gallium and zinc. High conversions were obtained and the aromatic selectivity was above 50% when the gallium loading was 0.5 wt%. For Zn/H-ZSM-5 catalysts the activity increased with increase in zinc loading. The 3%Zn/H-ZSM-5 was the most active catalyst attaining a conversion of 88% and aromatic selectivity above 40%. The impregnation of H-ZSM-5 with molybdenum led to a decrease in activity and aromatic selectivity. As the molybdenum content was increased the deactivation rate increased with time-on-stream. This may be attributed to less dispersion of molybdenum species in the H-ZSM-5 channels leading to the blockage of the pore and active sites. The NH3- TPD profiles suggested that an increase in the molybdenum content decreased the concentration of Brønsted acid sites hence decreased the activity of the H-SM-5 catalysts. The results obtained showed that Ga/H-ZSM-5 and Zn/H-ZSM-5 catalysts are good catalysts for the aromatization of n-hexane due to their dehydrogenation activity. The results on the effect of percentage XRD crystallinity (from 5 to 86%) of H-ZSM-5 on the activity of H-ZSM-5 modified by loading 2 wt% of metal showed that conversion of n-hexane increased with %XRD crystallinity. The Ga/H-ZSM-5 and Zn/H-ZSM-5 catalysts with %XRD crystallinity above 30% showed more aromatic selectivity than Mo/H-ZSM-5 catalysts. The Mo/H-ZSM-5 catalysts were more selective to the cracked products due to the absence of the dehydrogenation activity that is possessed by gallium and zinc metals. The effect of reaction temperature (between 500 and 600o) on the aromatization of n-hexane over H-ZSM-5 containing 2 wt% metal content was investigated. The activity of catalysts increased with temperature for the 1 hour on-stream studies and as the time-on-stream increased a decrease in activity was observed. But at 550oC Ga/H-ZSM-5 and Mo/H-ZSM-5 showed good stability with increase in time-on-stream. A rapid deactivation on Zn/H-SM-5 is associated with zinc leaving the catalyst bed

Transitioning Vocational Education and Training in Africa

EPDF and EPUB available Open Access under CC-BY-NC-ND licence. This book takes an expansive view of vocational education and training. Drawing on case studies across rural and urban settings in Uganda and South Africa, the book offers a new way of seeing this through an exploration of the multiple ways in which people learn to have better livelihoods. Crucially, it explores learning that takes place informally online, within farmers’ groups and in public and private education institutions

Transitioning Vocational Education and Training in Africa

EPDF and EPUB available Open Access under CC-BY-NC-ND licence. This book takes an expansive view of vocational education and training. Drawing on case studies across rural and urban settings in Uganda and South Africa, the book offers a new way of seeing this through an exploration of the multiple ways in which people learn to have better livelihoods. Crucially, it explores learning that takes place informally online, within farmers’ groups and in public and private education institutions

Transitioning Vocational Education and Training in Africa: A Social Skills Ecosystem Perspective

The transition to more just and sustainable development requires radical change across a wide range of areas and particularly within the nexus between learning and work. This book takes an expansive view of vocational education and training that goes beyond the narrow focus of much of the current literature and policy debate. Drawing on case studies across rural and urban settings in Uganda and South Africa, the book offers a new way of seeing this issue through an exploration of the multiple ways in which people learn to have better livelihoods. Crucially, it explores learning that takes place informally online, within farmers’ groups, and in public and private educational institutions. Offering new insights and ways of thinking about this field, the book draws out clear implications for theory, policy and practice in Africa and beyond

Non-oxidative conversion of methane into aromatic hydrocarbons over molybdenum modified H-ZSM-5 zeolite catalysts

Dehydroaromatization of methane (MDA) reaction was investigated over platinum modified Mo/H-ZSM-5 catalysts which were pre-carbided at 750 oC. The influence of platinum on the catalytic performance and product selectivity of Mo/H-ZSM-5 catalysts for the MDA reaction at 700 oC was studied. The presence of platinum led to a slight decrease in methane conversion. As the platinum loading increased, the methane conversion decreased further and the catalytic stability increased with time-on-stream (TOS) during the MDA reaction. Aromatic selectivities above 90% were obtained with catalysts containing low platinum loadings (0.5 and 1.0 wt.%), with benzene being the most prominent product. A decrease in coke selectivity and coke deposits was noted with the platinum modified Mo/H-ZSM-5 zeolite catalysts. A comparative study was performed to compare platinum, palladium and ruthenium promoted Mo/H-ZSM-5 zeolite catalysts with un-promoted Mo/H-ZSM-5. The ruthenium promoted catalyst proved to be superior in catalytic performance, with a higher methane conversion obtained than found for platinum promoted and palladium promoted Mo/H-ZSM-5 catalysts. Benzene selectivity of about 60% was obtained for ruthenium and palladium promoted Mo/HZSM- 5 catalysts and the total aromatic selectivity was maintained at 90%. TGA results showed a total reduction of 50% by weight of carbon deposited on the promoted Mo/H-ZSM-5 catalyst. Dehydroaromatization of methane was studied over tin modified Pt/Mo/HZSM-5 catalysts and compared to Pt/Mo/H-ZSM-5 catalyst at 700 oC. Addition of tin decreased the activity towards methane aromatization. However, the formation of aromatic compounds was favoured. The CO FT-IR adsorption and CO chemisorption techniques showed that the catalyst preparation method had an effect on the catalytic performance of tin modified Pt/Mo/H-ZSM-5 catalysts. High aromatic selectivity and low coke selectivity were obtained with co-impregnated and sequentially impregnated Pt/Sn catalysts. While a decrease in the formation rate of carbonaceous deposits is mainly dependent on the availability of platinum sites for the hydrogenation of carbon. The order of sequentially loading platinum and tin has an effect on the electronic and structural properties of platinum as shown by XPS and FT-IR studies. CO chemisorption and the FT-IR adsorption studies showed that addition of tin decreased the adsorption capacity of the platinum surface atoms. Catalyst preparation methods and successive calcination treatments affected the location of both tin and platinum atoms in the catalyst. Catalysts prepared by the coimpregnation method showed a good platinum dispersion, better than found for the sequentially impregnated catalysts. The MDA reaction was carried out at 800 oC over manganese modified H-ZSM-5 zeolite catalysts prepared by the incipient wetness impregnation method. The effect of a number of parameters on the catalytic performance and product selectivity was investigated, such as reaction temperature, manganese precursor-type, tungsten as promoter, manganese loading and use of noble metals. The study of the effect of reaction temperature showed that the methane conversion increased linearly with increase in reaction temperature from 700 to 850 oC. The selectivity towards aromatic compounds (of about 65%) was attained for the reactions performed at 750 and 800 oC. Formation rate of carbonaceous deposits increased linearly with increase in reaction temperature. The use of different manganese precursors to prepare Mn/H-ZSM-5 catalysts had an effect on both the catalytic behaviour and the product distribution. High catalytic activities were obtained for the catalysts prepared from Mn(NO3)2 and MnCl2 salts. However, the product distribution was significantly different, with the Mn(NO3)2 catalyst being more selective towards aromatic compounds while the MnCl2 catalyst was more selective toward coke. The effect of manganese loading was studied at 800 oC and an optimum catalyst activity was obtained at 2 and 4 wt.% manganese loadings. The aromatic selectivity above 70% and coke selectivity of 20% were obtained for a 2 wt.% loaded catalyst. Addition of tungsten as a promoter onto the 2 wt.% loaded catalyst (2Mn/H-ZSM-5) lowered the catalytic activity but the catalyst remained fairly stable with increase in TOS. Tungsten modified catalysts favoured the formation of carbonaceous deposits over aromatic compounds. TGA results showed a coke deposit of 164 mg/g.cat, an 88% increase in coke deposit when tungsten was used a promoter. Noble metals were added to reduce the total amount of coke on the tungsten modified Mn/H-ZSM-5 catalysts. The presence of a noble metal favoured the formation of aromatic compounds and suppressed the formation of coke. Platinum and ruthenium promoted catalysts were the active catalysts and aromatic selectivity increased from 12% to 55% and 46% respectively. A reduction in the total amount of coke deposit on the platinum promoted catalyst (42%) and the ruthenium promoted catalyst (31%) was noted

Dehydroaromatization of methane over noble metal loaded Mo/H-ZSM-5 zeolite catalysts

Abstract Dehydroaromatization of methane (MDA) reaction was investigated over platinum modified Mo/H-ZSM-5 catalysts which were pre-carbided at 750 °C. The influence of platinum on the catalytic performance and product selectivity of Mo/H-ZSM-5 catalysts for the MDA reaction at 700 °C were studied. The presence of platinum led to a slight decrease in methane conversion from 7.5 to 4.2%. Aromatic selectivities above 90% were obtained with catalysts containing low platinum loadings (0.5 and 1.0 wt.%), with benzene being the most prominent product. A decrease in coke selectivity and coke deposits was noted with the platinum modified Mo/H-ZSM-5 zeolite catalysts. A comparative study was performed to compare platinum, palladium and ruthenium promoted Mo/H-ZSM-5 zeolite catalysts with un-promoted Mo/H-ZSM-5. The ruthenium promoted catalyst proved to be superior in catalytic performance, with a higher methane conversion obtained than that found for platinum promoted and palladium promoted Mo/H-ZSM-5 catalysts. Benzene selectivity of about 60% was obtained for ruthenium and palladium promoted Mo/H- ZSM-5 catalysts and the total aromatic selectivity was maintained at 90%. TGA results showed a total reduction of 50% by weight of carbon deposited on the promoted Mo/H-ZSM-5 catalyst. Graphic abstrac

Photocatalytic Degradation of Methylene Blue and Ortho-Toluidine Blue: Activity of Lanthanum Composites LaxMOy (M: Fe, Co, Ni)

Lanthanum (La) nanocomposites LaFeO3, LaNiO3, and LaCoO3 were synthesized using a sol-gel method, and different La to-metal (Fe, Ni, or Co) ratios were attained using various concentrations of salts. The resulting composites were calcined at 540 °C and characterized by XRD, SEM-EDX, FT-IR spectroscopy, XPS, thermogravimetric analysis (TGA), and PL spectroscopy. The activity of the lanthanum composites (LaFeO3, LaNiO3, and LaCoO3) was studied using the photocatalytic degradation of methylene blue (MB) and ortho-toluidine blue (o-TB) under visible light with a wavelength below 420 nm. The change in the concentration of dyes was monitored by using the UV-Vis spectroscopy technique. All composites appeared to have some degree of photocatalytic activity, with composites possessing an orthorhombic crystal structure having higher photocatalytic activity. The LaCoO3 composite is more efficient compared with LaFeO3 and LaNiO3 for both dyes. High degradation percentages were observed for the La composites with a 1:1 metal ratio

Photocatalytic Degradation of Methylene Blue and Ortho-Toluidine Blue: Activity of Lanthanum Composites La_xMO_y (M: Fe, Co, Ni)

Lanthanum (La) nanocomposites LaFeO3, LaNiO3, and LaCoO3 were synthesized using a sol-gel method, and different La to-metal (Fe, Ni, or Co) ratios were attained using various concentrations of salts. The resulting composites were calcined at 540 °C and characterized by XRD, SEM-EDX, FT-IR spectroscopy, XPS, thermogravimetric analysis (TGA), and PL spectroscopy. The activity of the lanthanum composites (LaFeO3, LaNiO3, and LaCoO3) was studied using the photocatalytic degradation of methylene blue (MB) and ortho-toluidine blue (o-TB) under visible light with a wavelength below 420 nm. The change in the concentration of dyes was monitored by using the UV-Vis spectroscopy technique. All composites appeared to have some degree of photocatalytic activity, with composites possessing an orthorhombic crystal structure having higher photocatalytic activity. The LaCoO3 composite is more efficient compared with LaFeO3 and LaNiO3 for both dyes. High degradation percentages were observed for the La composites with a 1:1 metal ratio

Transitioning Vocational Education and Training in Africa: A Social Skills Ecosystem Perspective

The transition to more just and sustainable development requires radical change across a wide range of areas and particularly within the nexus between learning and work. This book takes an expansive view of vocational education and training that goes beyond the narrow focus of much of the current literature and policy debate. Drawing on case studies across rural and urban settings in Uganda and South Africa, the book offers a new way of seeing this issue through an exploration of the multiple ways in which people learn to have better livelihoods. Crucially, it explores learning that takes place informally online, within farmers’ groups, and in public and private educational institutions. Offering new insights and ways of thinking about this field, the book draws out clear implications for theory, policy and practice in Africa and beyond