Thesis (Ph.D.)--University of Nebraska-Lincoln, 2009. / Title from title screen (site viewed October 13, 2009). PDF text: xiv, 183 p. : ill. (some col.) ; 1 Mb. UMI publication number: AAT 3358961. Includes bibliographical references. Also available in microfilm and microfiche formats.

The pressing need for clean renewable energy sources has aroused worldwide research interest on the exploration of biofuels produced from lignocellulosic feedstock (e.g. forestry or agricultural residues and municipal wastes). The general absence of cost-effective method to overcome the recalcitrant nature of cellulosic biomass is the major challenge for the industrialization of this so-called second-generation biofuel. With the purpose to enhance our understanding of the fundamental mechanism of thermophilic microbial cellulose conversion process, we used culture-independent metagenomic analysis based on Next Generation Sequencing to explore the physiological ecology of thermophilic cellulolytic microbial community and more importantly to discover metabolic potentials. During the enrichment of thermophilic cellulolytic consortium, noticeable effects of co-substrate and pH was observed and subsequently investigated. Based on the community structure revealed by 16S rRNA gene sequencing at various pH values, we concluded that keeping pH higher than 6.0 was crucial to maintain effective cellulose conversion because the growth of Thermoanaerobacterium over other more efficient cellulolytic populations could be practically avoided. Given in mind that uncharacterized microbial populations may possess critical enzymatic components that are essential for the breakdown of cellulosic feedstock, gene-centric metagenomic pipeline was developed to discover genes that are functionally beneficial for thermophilic cellulose hydrolysis. Aside from that, metagenomic gene mining based on functional prediction using HMM (Hidden Markov Model) showed higher positive ratio in identifying novel carbohydrate-active genes than that of functional screening. Without cultivation, near complete genomes of the major thermophilic cellulose degraders were recovered from the metagenome by a gene binning pipeline combining tetranucleotide frequency based primary k-means clustering and subsequent scaffolding with paired-end relationship between two reads (sequences). Furthermore, by quantifying the transcriptional activities of various carbohydrate-active genes in the metatranscriptome of the enriched thermophilic cellulose-degrading consortium, we disclosed significance of enzymes of GH09 and GH48 which had been underestimated by previous metagenomic studies. Eventually, metagenomic survey of various sludge samples collected at specific operational conditions helped to confirm the metabolism potential of thermophilic sludge in cellulose up taking by possessing more enzymes of GH05 and GH04 families. / published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

Thesis (Ph. D.)--University of Wisconsin--Madison, 1992. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 330-341).

With the gradual depletion of the non-renewable fossil fuel resources and the emerging environmental concerns, the need of exploring renewable synthesis routes of our daily basic stocks is rising. Due to the large contribution to the global primary energy (up to 40% in some countries), biomass has recently been advocated to be one of the most promising alternatives for fossil fuel. This thesis focuses on the catalytic transformations of biomass or biomass derived molecules into valuable small alcohols such as methanol, ethanol, and propanol, which can be used as both fuel and chemical synthesis intermediates. Novel catalysts with high activity and selectivity toward target products are desperately required in the development of renewable chemical synthesis routes. In the past 200 years, platinum metal catalysts have been widely used in the industry. But nowadays, Pd is attracting increasing attentions due to (i) its similar physicochemical properties to those of Pt, (ii) its higher natural abundance than Pt. Alloying has been demonstrated as an effective method in enhancing the catalytic properties of noble metals. In this thesis, a new and facile method for the preparation of supported bimetallic NPs with tunable compositions is developed. Through the establishment of a type II hetero-junction in support, controllable amounts of metallic atoms can be derived from the reduction of the metal oxide support, with the assistance of a supported noble metal. A series of extremely small Pd-based bimetallic NPs with a variety of modifier atoms at tunable compositions, namely PdFe, PdCo, PdNi and PdZn, have been synthesized by this method. These novel bimetallic NPs are applied to the catalytic conversion of biomass or biomass derived molecules containing repeating vicinal diol units. It is demonstrated that the catalytic performance of Pd in bimetallic phase is governed by the d-band structure. The high degree of d-band filling and high d-band center position favour the selective C-O cleavage in hydrogenolysis of vicinal diol units. On the other hand, the selective C-C cleavage can be achieved by lowering the d-band filling of the Pd-based bimetallic NPs. The specificity of C-C bond rupture over that of C-O increases in order of PdZn < PdNi < PdCo < PdFe, with progressive d-band filling reduction, eventually reaches 95% in a series of vicinal diols hydrogenolysis. As a result, small alcohols are produced with high selectivity as the degradation products of biomass molecules when PdFe bimetallic NPs are employed as catalyst. Conversely, by incorporating Co atoms at high concentration, PdCo exhibits a high selectivity in breaking C-O bond of ethylene glycol due to the raised d-band center position and gives ethanol as the main product. Pd@Zn bimetallic NPs with an imperfect core(Pd)-shell(Zn) structure were used in a methanol synthesis route from biomass transformation via CO₂ hydrogenation (CO₂/H₂ is produced from low temperature reforming of biomass resource). The Zn shell not only enhances the catalytic activity of Pd metal towards methanol synthesis, but also suppresses the reverse water gas shift (RWGS) reaction in which CO is produced as a by-product. Methanol can be produced as the main product over CO on the Zn rich Pd@Zn surface, even at low pressure. The methanol turnover frequency (TOF) on the exposed Pd site reaches 1.9 ×10^-1 s^-1 with a selectivity of 70% at 2 MPa. The enhancement is attributed to the increasing d-band filling of Pd@Zn bimetallic NPs by the progressive decoration of Zn on Pd surface, which selectively stabilizes the precursor of methanol (HCOO) over that of CO (COOH). Also, the PdZn catalyst with high ability in dissociating H2 reduces the activation barrier for methanol synthesis. The results presented in this thesis, for the first time, signify the possibility of fine-tuning of product specificity of biomass conversion simply by rationally modifying the electronic properties of the Pd-based catalysts. More importantly, these catalysts will help to diversify the energy generation and relieve our dependence on fossil fuels.

Biomass is a natural resource that is both abundant and sustainable. Its efficient utilization has long been the focus of research and development efforts with the aim to substitute it for fossil-based feedstock. In addition to the production of biofuels (e.g., ethanol) from biomass, which has been to some degree successful, its conversion to high value-added chemicals is equally important. Among various biomass conversion pathways, catalytic conversion is usually preferred, as it provides a cost-effective and eco-benign route to the desired products with high selectivities. The research of this thesis is focused on the conversion of biomass to various chemicals of commercial interest by selective catalytic oxidation. Molecular oxygen is chosen as the oxidant considering its low cost and environment friendly features in comparison with commonly used hydrogen peroxide. However, the activation of molecular oxygen usually requires high reaction temperatures, leading to over oxidation and thus lower selectivities. Therefore, it is highly desirable to develop effective catalysts for such conversion systems. We use kegging-type heteropoly acids (HPAs) as a platform for catalysts design because of their high catalytic activities and ease of medication. Using HPA catalysts allows the conversion taking place at relatively low temperature, which is beneficial to saving production cost as well as to improving the reaction selectivity. The strong acidity of HPA promotes the hydrolysis of biomass of giant molecules (e.g. cellulose), which is the first as well as the most difficult step in the conversion process. Under certain circumstances, a HPA combines the merits of homogeneous and heterogeneous catalysts, acting as an efficient homogeneous catalyst during the reaction while being easily separated as a heterogeneous catalyst after the reaction. We have successfully applied HPAs in several biomass conversion systems. Specially, we prepared a HPA-based bi-functional catalyst (Au/Cs2HPW12O40) that enabled the selective conversion of cellobiose to gluconic acid with a very high yield of 96.4% (Chapter II); we realized a direct oxidative conversion of cellulose to glycolic acid (yield of 49.3 %) in a water medium for the first time, by using a phosphomolybdic acid catalyst (chapter III); we found that a vanadium-substituted phosphomolybdic acid catalyst (H4PVMo11O40) is capable of converting various biomass-derived substrates to formic acid and acetic acid with high selectivity, and under optimized reaction conditions, high yield of formic acid (67.8%) can be obtained from cellulose (chapter IV); we discovered that the vanadium-substituted phosphomolybdic acids can also selectively oxidize glycerol, a low-cost by-product of biodiesel, to formic acid, and interestingly this conversion can be performed in highly concentration aqueous solution (glycerol: water = 50: 50), giving rise to exceptionally high conversion efficiency (chapter V). These results reveal that HPAs are useful and suitable catalysts for selective oxidation of biomass, and that the reaction pathway is largely determined by the type of addenda atom in the HPA catalyst. The optimization of the reaction conditions and processes in these systems are also discussed in this thesis.

No description available.

Thesis (M.S.)--Auburn University, 2007. / Abstract. Vita. Includes bibliographic references (ℓ. 80)

Thesis (Ph.D.)--Baylor University, 2007. / In abstract "5, 2, 9, 8, 12, 25, and 3" are subscript. In abstract "5 and 2 are superscript. Includes bibliographical references (p. 180-187).

Thesis (Ph. D.)--University of Virginia, 2007. / Includes bibliographical references. Also available online through Digital Dissertations.

Thesis (Ph.D.)--Kansas State University, 2008. / Advisers: Donghai Wang, Scott Bean. Includes bibliographical references.