title: Preparation of mesoporous solids containing encapsulated metal species of technological interest

authors: Xu, Sheng

subjects: mesoporous solids

abstract: The advent of mesoporous silicas such as MCM-41 has provided new opportunities for research into supported metal catalysis. The loading of metals into framework structures and particularly into the pores of porous molecular sieves, has long been of interest because of their potential catalytic activity. The larger pore sizes of mesoporous silicas allow for the possibility of preparing dispersions of metal/metal oxide particles within the pores while still allowing access by reagent molecule. In standard fabrication processes, metal particle size is not well controlled. Most studies of metal/metal oxide loaded mesoporous silicas report metal/metal oxide particles larger than the pore diameter. In the present work, new methods of preparing metal loaded systems have been developed to facilitate a more even dispersion of the metal. The metals were loaded as readily decomposed organometallic complexes so the chemistry involved in forming the metal/metal oxide particles minimized possible sintering effects. New synthetic routes were developed to facilitate loading into the pores or the framework of the silica matrix. An optimised acid synthetic route for preparing MCM-41 was used throughout. The acid concentration, surfactant concentration, reaction time and stirring rate, all of which have strong influence on the morphology and structure of the mesoporous materials under acidic synthetic conditions, were optimised to give systems of maximum surface area while exhibiting regular pore structures and good stability. The refined reaction conditions of high stirring speeds, low surfactant concentration, high acid concentrations and short reactions times developed in the present work represent important improvements in synthetic methodology giving stable, well ordered, small pore, thick walled and high surface area products. Single metal and mixed metal organometallic complexes were loaded into the preformed mesoporous supports by a modified imbibing method and then decomposed to prepare metal and mixed metal nanoparticles within the structures. However, loading by this method caused disordering and destruction of the MCM-41 porous supports, the broadening of the XRD diffraction lines, and the significant reduction of pore size, pore volume and specific surface area. A major contribution of the current work has been the development of two methods for controlling the loading of metals into the structures during synthesis. These methods offer the significant advantages of loading without structural effects and yielding producing systems where surface area increased rather than decreased with loading. By the M method, a hydrophobic organometallic complex was incorporated within the micelle system formed by the surfactant, cetyltrimethylammonium bromide. This micelle system containing the organometallic complex forms the template for the pores during the sol-gel formation of the mesoporous solids. Incorporation of the metal within the micelle facilitates the dispersion of the metal throughout the surfactant phase filling the pores of final precursor material. Calcining to remove the organic material favours leaving the metal or metal oxide in the form of small particles widely and uniformly dispersed in the mesoporous channels. By the T method, organometallic molecules are dissolved in the Si(OEt)4 of the synthesis mixture. Calcining the organic material from the resulting precursor favours leaving the metal or metal oxide in a widely and uniformly dispersed state in the walls of mesopores. The synthetic methods developed were extended to prepare mixed metal nanoparticles of defined composition using single-source mixed metal organometallic compounds. In this way novel mixed metal (Mo/Fe and Mo/Co) phases with compositions determined by the stoichiometry of the initial mixed metal complex were produced and characterised. The nature of the metal/metal oxide particles was studied by XRD and TEM. At the metal loadings obtained (ranging up to 4%) crystalline metal and metal oxide particles should be readily detected. The absence of well defined XRD peaks characteristic of the metal or metal oxides in any of the samples provided evidence that the metals after calcining were well dispersed, with particles sizes less than a few nm and too small to give diffraction signals. TEM studies revealed a clearly defined hexagonal pore structure with pore diameters of approximately 2 nm but gave no evidence of metal particles larger than the resolving power of the instrument (approximately 1 nm).

text: Preparation of mesoporous solids containing encapsulated metal species of technological interest The advent of mesoporous silicas such as MCM-41 has provided new opportunities for research into supported metal catalysis. The loading of metals into framework structures and particularly into the pores of porous molecular sieves, has long been of interest because of their potential catalytic activity. The larger pore sizes of mesoporous silicas allow for the possibility of preparing dispersions of metal/metal oxide particles within the pores while still allowing access by reagent molecule. In standard fabrication processes, metal particle size is not well controlled. Most studies of metal/metal oxide loaded mesoporous silicas report metal/metal oxide particles larger than the pore diameter. In the present work, new methods of preparing metal loaded systems have been developed to facilitate a more even dispersion of the metal. The metals were loaded as readily decomposed organometallic complexes so the chemistry involved in forming the metal/metal oxide particles minimized possible sintering effects. New synthetic routes were developed to facilitate loading into the pores or the framework of the silica matrix. An optimised acid synthetic route for preparing MCM-41 was used throughout. The acid concentration, surfactant concentration, reaction time and stirring rate, all of which have strong influence on the morphology and structure of the mesoporous materials under acidic synthetic conditions, were optimised to give systems of maximum surface area while exhibiting regular pore structures and good stability. The refined reaction conditions of high stirring speeds, low surfactant concentration, high acid concentrations and short reactions times developed in the present work represent important improvements in synthetic methodology giving stable, well ordered, small pore, thick walled and high surface area products. Single metal and mixed metal organometallic complexes were loaded into the preformed mesoporous supports by a modified imbibing method and then decomposed to prepare metal and mixed metal nanoparticles within the structures. However, loading by this method caused disordering and destruction of the MCM-41 porous supports, the broadening of the XRD diffraction lines, and the significant reduction of pore size, pore volume and specific surface area. A major contribution of the current work has been the development of two methods for controlling the loading of metals into the structures during synthesis. These methods offer the significant advantages of loading without structural effects and yielding producing systems where surface area increased rather than decreased with loading. By the M method, a hydrophobic organometallic complex was incorporated within the micelle system formed by the surfactant, cetyltrimethylammonium bromide. This micelle system containing the organometallic complex forms the template for the pores during the sol-gel formation of the mesoporous solids. Incorporation of the metal within the micelle facilitates the dispersion of the metal throughout the surfactant phase filling the pores of final precursor material. Calcining to remove the organic material favours leaving the metal or metal oxide in the form of small particles widely and uniformly dispersed in the mesoporous channels. By the T method, organometallic molecules are dissolved in the Si(OEt)4 of the synthesis mixture. Calcining the organic material from the resulting precursor favours leaving the metal or metal oxide in a widely and uniformly dispersed state in the walls of mesopores. The synthetic methods developed were extended to prepare mixed metal nanoparticles of defined composition using single-source mixed metal organometallic compounds. In this way novel mixed metal (Mo/Fe and Mo/Co) phases with compositions determined by the stoichiometry of the initial mixed metal complex were produced and characterised. The nature of the metal/metal oxide particles was studied by XRD and TEM. At the metal loadings obtained (ranging up to 4%) crystalline metal and metal oxide particles should be readily detected. The absence of well defined XRD peaks characteristic of the metal or metal oxides in any of the samples provided evidence that the metals after calcining were well dispersed, with particles sizes less than a few nm and too small to give diffraction signals. TEM studies revealed a clearly defined hexagonal pore structure with pore diameters of approximately 2 nm but gave no evidence of metal particles larger than the resolving power of the instrument (approximately 1 nm).

year: 2011

title: Spray Dryer Exhaust Heat Recovery: A Techno-economic Assessment Model

authors: Walmsley, Timothy Gordon

abstract: This paper discusses the spray dryer exhaust heat recovery in Milk Power Production.

text: Spray Dryer Exhaust Heat Recovery: A Techno-economic Assessment Model This paper discusses the spray dryer exhaust heat recovery in Milk Power Production.

year: 2014-08-26

title: Understanding the Happiness of Māori and the Role of Consumption: Experiences of the Millennial Generation

authors: de Thierry, Ebony

subjects: Māori Well-Being

abstract: Happiness is commonly perceived as the ideal state of being for  all of human kind. Although a universal definition of the term remains elusive, happiness is a goal that everybody wants to achieve. In understanding the different aspects that shape happiness, the literature has shown that this can vary depending on the cultural context. As such, this study investigates the essence of happiness as it is experienced by Māori. In understanding the experiences of the Millennial generation, the role that consumption plays is also explored. This group of young adults have been raised in an era when consumerism and cultural revitalisation are the norm.  

This investigation was guided by hermeneutic phenomenology using a kaupapa Māori research perspective. Through this, thirteen young Māori individuals were interviewed to gain their experiences of happiness. Photo elicitation techniques were utilised as a means to facilitate these interviews. Stories of the participants’ experiences of happiness were crafted and then analysed to explore the role of consumption.

Findings show that the happiness of Māori is shaped by the five themes of; sense of belonging, whānau and relationships, spirituality, achievement and success, and sense of freedom. These themes interrelate as they are underpinned by the collective values of Māori. In particular, the aspects of spirituality and sense of belonging appear to be specific to the Māori realm. These are based on customs, values and beliefs that are inherited from our ancestors yet are still prevalent today. In terms of consumption, happiness can be positively linked to experiential consumption. In this case, it can play three different roles on the happiness of Māori through either; a direct connection, an indirect connection, or a negative connection. For Māori, consumption is more likely to have an indirect connection. This implies that it is able to facilitate, maintain and enhance happiness, but is not essential to creating these feelings. This investigation contributes to the literature in four ways. First, this study serves as a starting point to developing a comprehensive framework of happiness that is specific to the culture, views and values of Māori. This will assist Māori through ensuring that they are accurately represented in policies, frameworks and statistics. Second, it proposes five guidelines for Māori which suggest how they can maximise happiness through consumption. Third, this study provides a more up-to-date understanding of the happiness of Māori at the individual level whilst incorporating the impact of collective values. Marketers, researchers and practitioners can utilise this information in an attempt to aid in improving the happiness of Māori society. Finally, it shows that consumption can continue to be positively related to happiness once basic needs have been met. The positive role that consumption can play on happiness is identified, showing that marketers and consumers can work together to achieve happiness.

text: Understanding the Happiness of Māori and the Role of Consumption: Experiences of the Millennial Generation Happiness is commonly perceived as the ideal state of being for  all of human kind. Although a universal definition of the term remains elusive, happiness is a goal that everybody wants to achieve. In understanding the different aspects that shape happiness, the literature has shown that this can vary depending on the cultural context. As such, this study investigates the essence of happiness as it is experienced by Māori. In understanding the experiences of the Millennial generation, the role that consumption plays is also explored. This group of young adults have been raised in an era when consumerism and cultural revitalisation are the norm.  

This investigation was guided by hermeneutic phenomenology using a kaupapa Māori research perspective. Through this, thirteen young Māori individuals were interviewed to gain their experiences of happiness. Photo elicitation techniques were utilised as a means to facilitate these interviews. Stories of the participants’ experiences of happiness were crafted and then analysed to explore the role of consumption.

Findings show that the happiness of Māori is shaped by the five themes of; sense of belonging, whānau and relationships, spirituality, achievement and success, and sense of freedom. These themes interrelate as they are underpinned by the collective values of Māori. In particular, the aspects of spirituality and sense of belonging appear to be specific to the Māori realm. These are based on customs, values and beliefs that are inherited from our ancestors yet are still prevalent today. In terms of consumption, happiness can be positively linked to experiential consumption. In this case, it can play three different roles on the happiness of Māori through either; a direct connection, an indirect connection, or a negative connection. For Māori, consumption is more likely to have an indirect connection. This implies that it is able to facilitate, maintain and enhance happiness, but is not essential to creating these feelings. This investigation contributes to the literature in four ways. First, this study serves as a starting point to developing a comprehensive framework of happiness that is specific to the culture, views and values of Māori. This will assist Māori through ensuring that they are accurately represented in policies, frameworks and statistics. Second, it proposes five guidelines for Māori which suggest how they can maximise happiness through consumption. Third, this study provides a more up-to-date understanding of the happiness of Māori at the individual level whilst incorporating the impact of collective values. Marketers, researchers and practitioners can utilise this information in an attempt to aid in improving the happiness of Māori society. Finally, it shows that consumption can continue to be positively related to happiness once basic needs have been met. The positive role that consumption can play on happiness is identified, showing that marketers and consumers can work together to achieve happiness.

year: 2012