Heterogeneous gold, palladium and copper based catalysts for liquid phase oxidation of methane

The oxidation of lower alkanes especially methane to methanol under mild reaction conditions is one of the most challenging task for industry and academia. At present, indirect utilisation via synthesis gas is the only commercially viable process for methanol production. Therefore, this study intends to investigate the direct oxidation of methane to methanol using a novel low temperature approach. Recently, gold based supported catalysts have been found to be highly effective oxidation catalysts where a number of important discoveries have been made such as in hydrogen peroxide synthesis and selective oxidation of alcohols to aldehydes. Due to these recent advances, further work into the oxidation of carbon-hydrogen bonds especially methane by gold and gold-palladium alloyed nanoparticles was the central topic of this study. As a proof of concept for the following studies, oxidation of primary C-H bonds in toluene and toluene derivatives were carried out in a high pressure stirred autoclave with molecular oxygen as oxidant. It was evident that Au-Pd supported catalyst is capable in oxidising primary C-H bonds on toluene and toluene derivatives at lower temperature with high catalytic activity based on turnover number (TON) compared to available heterogeneous catalysts reported in literature. However, these catalysts are ineffective in the oxidation of methane with oxygen under mild conditions with water as solvent and temperature below 90ᵒC. In view of this, hydrogen peroxide has been used as oxidant and it was shown that Au-Pd supported nanoparticles are active for the oxidation of methane giving high selectivity to methanol especially in the reactions carried out with hydrogen peroxide generated using an in-situ approach. Methane oxidation reactions were carried out in aqueous medium. The main products were methanol, methyl hydroperoxide and only carbon dioxide as overoxidation product. Investigations of reaction conditions such as concentration of oxidant, reaction time, reaction temperature and pressure of methane were investigated. It was found that the activity and selectivity of the catalyst was highly dependant on these variables. Oxygenate productivity was found to increase by increasing the H2O2 or H2O2 concentration and methane pressure. Longer reaction times were detrimental to the methanol selectivity where overoxidation reaction occurred. Interestingly, the Au-Pd catalytic system was able to oxidise methane to methanol at temperatures as low as 2ᵒC. The applicability of the developed catalytic system was tested on ethane oxidation reaction and it successfully produced ethanol as the major product. The oxygenate productivity was higher as compared to methane due to the solubility factor and the difference in the strength of carbon-hydrogen bonds. The catalyst preparation method and pretreatment were shown to be very important in the formation of active catalysts. The Au-Pd alloy having Au core-palladium shell structure with PdO dominance on the surface and bigger particle size was preferred than analogue catalyst consists of Au and Pd in metallic state with smaller particle size. In addition to that, the choice of support is crucial and this study discovered TiO: as a preferred support where it could assist in stabilising the active hydroperoxy species. The Au:Pd ratio was also found to be an important variable, and equal weight ratio between Au and Pd was shown to be the optimised ratio for methane oxidation either using addition of H2O2 or in-situ H2O2 approach. The synergistic effect of Au and Pd was confirmed by superior catalytic activity compared to monometallic catalysts. Reaction mechanism was proposed and it was based on catalytic evaluation data, stability of the products and oxidation with radical scavengers. The proposed mechanism was in line with the theoretical modelling studies on similar catalytic systems. Optimisation of Au based supported catalyst with copper as co-metal supported on TiO2 was shown to improve the oxygenate productivity and methanol selectivity as well as enhanced the H2O2 utilisation. In particular, trimetallic 5wt%AuPdl.0wt%Cu/TiO2 synthesised via impregnation method and calcined in static air gave more than double turn over frequency (TOF = 1.404) with methanol selectivity around 83% as compared to bimetallic 5wt%Au-Pd/TiO2 catalyst (TOF = 0.692, methanol selectivity = 49%). It was suggested in this study that copper is responsible in enhancing the formation of intermediate methyl hydroperoxide species and in some extent to block the non-selective sites for hydrogen peroxide decomposition and hydrogenation by disrupting the surface structure of Au-Pd alloy whilst at the same time maintaining the active sites (Au-Pd alloy) responsible for selective formation of methanol. The oxidation state of copper was shown to be the main factor in controlling the catalytic activity and selectivity. Copper in a combination of multiple oxidation states was preferred than single oxidation state

Transesterification of Waste Cooking Oil using Calcium Loaded on Deoiled Spent Bleaching Clay as A Solid Base Catalyst

Waste cooking oil has a high potential as a raw material in biodiesel production due to its abundant availability and cheapest among other feedstock. Hence transesterification reaction is carried out using waste cooking oil in this research. The objective of this study is to synthesize and characterize the catalyst. On the other hand, deoiled spent bleaching clay impregnated with 40% CaO utilized as a catalyst. Optimization was carried out on methanol to oil molar ratio (6:1-24:1), catalyst loading (3-10 wt.%) and reaction duration (2-10 h). The catalyst of deoiled spent bleaching clay doped with 40% CaO was prepared by wet impregnation method and calcined at 500 °C for 4 hours. The catalyst shows high activity under optimum condition of 5 hours of reaction time, 12:1 of methanol to oil molar ratio with 7 wt.% of catalyst. The transesterification yields 84.7% methyl ester. Therefore, this catalyst has potential to be used in the transesterification of waste cooking oil in producing biodiesel due to its high activity

Kinetic and Thermodynamics of Methylene Blue Adsorption onto Zero Valent Iron Supported on Mesoporous Silica

Zero valent iron supported on mesoporous silicanano particles (NZVI/MSNs) was prepared by the aqueous phase borohydride reduction methods. Prior to the reduction, mesoporous silica nanoparticles (MSNs) were prepared through the activation of fumed silica with concentrated HCl by refluxing at 90 °C. FTIR, XRD, FESEM, EDX and BET were used to characterize theadsorbents prepared. BET surface areas of MSNs, NZVI, and NZVI/MSNs were 126, 41, and 72 m2/g for, respectively. The performance of NZVI/MSNs as adsorbent was examined by adsorption of methylene blue (MB), performed in series of batch experiments. In the kinetic studies, pseudo first order and pseudo second order kinetic models were examined. The pseudo second order equation provided the best fit with the experimental data. Thermodynamic studies indicated that the adsorption process is endothermic with ΔH° was 90.53 kJ/mol. Positive ΔS° (300 J/mol) and negative ΔG° (-6.42 kJ/mol) was recorded, indicating the spontaneous of the adsorption process and naturally favorable.

Sustainability and economic evaluation of Microalgae

The enhancement of the atmospheric greenhouse effect due to the increase in the atmospheric greenhouse gases is often considered as responsible for global warming. Several analyses have been made on the key issues of scientific understanding of contemporary global climate change. Air pollution are directly related with climate changes and it has been increasing the potential of ecosystems and human health risks. The policy and scientific assessments to climate change included the consideration of the risks and expressed climatic events. Microalgae has been identified as one of the potential feedstock for various bio product production since its cultivation requires less cropland compared to conventional oil crops and the high growth rate. The potential of microalgae to produce multiple bio based products in a biorefinery framework. The integration of emerging biorefineries is potential solution to mitigate the threat of climate change, global warming and food insecurity

Low Metal Loading Palladium Mixed-Oxides Catalyst for the Synthesis of Glycerol Carbonate

Glycerol carbonate can be readily synthesized from glycerol and urea catalyzed by PdZnO, PdSnO2, SnO2, and ZnO. The superior catalytic activity of ZnO over SnO2 is mainly due to basicity property. The incorporation of low metal loading of Pd on both SnO2 and ZnO produced higher yield of glycerol carbonate to bulk material counterpart. In addition, the sol-gel technique was shown to have higher turn-over frequency (TOF) due to highly disperse Pd with small crystallite size

The Effect of Iron (II) Chloride in Microalgae Cultivation for Bio-Oil Extraction

The world is facing a problem regarding the use of petroleum fuels that has led to a search for a suitable alternative fuel source. Researchers have come up with the idea of producing biofuel to overcome this problem. In this study, microalgae were explored as a high potential feedstock to produce biofuel. In order to produce a large quantity of biofuel with low cost at a short time, the manipulation of nutrients is a factor in microalgae cultivation. In this study, Iron (II) Chloride (FeCl2) was added to the nutrients to initiate a stressful condition during growth which contributes to the produce of lipid. Isolated microalgae species were identified as Scenedesmus sp. During mass cultivation, the microalgae cultures were scaled up to 2 L of culture. Three flasks of microalgae culture were labelled with S1, S2, and S3. Flask S1 acts as a control without the addition of FeCl2, while another two flasks acted as experimental flasks. Flask S2 was supplemented with 0.5 mg FeCl2 while Flask S3 was supplemented with 1.0 mg of FeCl2. With the addition of Iron (II) Chloride, microalgae entered a stationary phase at day 9 and day 10 as compared to the control flask which enters the stationary phase at day 7. This also affects the dry weight. Flask 3 produces 0.8658 g of microalgae powder compared to Flask 1 and 2 which produced 0.4649 g and 0.5357 g respectively. Lipid analysis was done by using GCMS and GC-FID. Flask 3 produced various types of fatty acids which can be used for biodiesel production compared to other cultivates. In Flask 1, docosanoic acid which is a saturated fatty acid was detected. While in Flask 2 (S2), with the addition of 0.5 mg of FeCl2, docosapentaenoic acid was produced. In the last flask which involved the addition of 1.0 mg of FeCl2, more fatty acid was detected. In GC-FID data, 6 types of fatty acids were detected. Linolein acid, linolenic acid, stearidonic acid, docosapentaenoic acid, docosahexaenoic acid and docosanoic acid were produced at different retention times. Most of the fatty acids produced are polyunsaturated fatty acid (PUFA). In transesterification, the fatty acid reacts with methanol and acid catalyst. The reaction produces fatty acid methyl ester. In Flask 1, the control flask, without the addition of FeCl2, no fatty acid methylesters (FAME) was produced. However, in Flask 2 and 3 which were added 0.5mg FeCl2 and 1.0 mg FeCl2, n-hexadecanoic acid methyl ester which is also known as palmitic acid was produced. Palmitic fatty acid can be used for biodiesel production

Plant extracts: Nanoparticle sources

Nanoparticles (NPs) (usually in dimensions of 1–100 nm) have been proven, throughnumerous research findings, to have excellent properties in term of physiochemical, anti-fungal, chemical, catalytic, thermal conduction, mechanical, electrical, optical, and manymore. NPs have vital roles in agro-production and protecting crops from diseases,both directly and indirectly, and they go even further to influence the soil microbialpopulation. At the nanoscale, the elementary understanding of chemical and physicalproperties is very distinctive. As such, research outputs at different scales will have dif-ferent interpretations that in turn radiate different properties, even for the same element.Owing to the superior qualities of NPs, research on them is intense, as many researchersare intensively working in the area. Nanoparticle utilization is glaring in many areas,including healthcare and cosmetics, food and feed, drug delivery systems, the space indus-try, electronics, optoelectronics, biomedical science, and ma

Lignin extractions from oil palm empty fruit bunch under pressurized and inert conditions

In this study, for the first time, lignin was extracted from palm oil empty fruit bunch (EFB) by using a pressurized reactor in the presence of deep eutectic solvents (DES). DES is prepared by mixing choline chloride and oxalic acid at a ratio of 1:1, successfully extracting around 30 wt.% of lignin under a relatively mild temperature. Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) are used in order to analyse lignin, whereas X-ray powder diffraction (XRD) is used to investigate the solid residues. FTIR analysis revealed the characteristics of lignin with a major functional group composed of phenolic, aliphatic hydroxyl and conjugated alkene in the FTIR spectra. This was further confirmed with thermal stability data using DSC. The crystallinity of the solid residue consisting of cellulose was observed to be affected by different temperatures, with the highest value (43.5 %) at 80 oC. The yield of lignin extracted under a pressurized and inert environment shows more than double the value of lignin as compared to the analogue process under atmospheric pressure and also shows comparable lignin yield with microwave assisted extraction systems. Thus, it provides a new, facile, and efficient approach to the delignification of lignocellulosic biomass

Isolation and characterization of bioactive compounds in medicinal plant centella asiatica and study the effects on fungal activities

Medicinal plants are sources of important therapeutic aids for alleviating human ailments. The present research investigation was carried out to study anti-fungal activity of C. asiatica were tested against C. albicans, Aspergillus niger, and Penicillium sp. using two methods, disc diffusion method and broth dilution method. C. asiatica crude methanol extract was found to be the most effective against fungal activity. Compared to disc diffusion, broth dilution was a more appropriate method to quantitatively determine the anti-Candida activity of plant extract, whereby the MIC values of the crude extracts was determined. The result from disc diffusion assay demonstrates that plant extracts have an inhibitory effect. However, the broth dilution method result reveal that C. asiatica crude methanol extract has lower MIC values, meaning it has more prove that C. asiatica has an anti-fungal effect. Bioactive analysis results reveled that bioactive compounds present in the leaf, stems, roots, and the whole plant extract from Centella asiatica are the major chemical constituents are n-Hexadecanoic acid (99%), cis-Vaccenic acid (91%), 5-Hydroxymethylfurfural (88%), Tetradecanoic acid (86%). Further study is required to find out the specific phytochemical which is responsible for its medicinal value