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- All Subjects: Arizona
- Creators: School of Sustainability
- Member of: Barrett, The Honors College Thesis/Creative Project Collection
Project 1 Abstract: Ethylene Oxychlorination
The current two-step process for the industrial process of vinyl chloride production involves CuCl2 catalyzed ethylene oxychlorination to ethylene dichloride followed by thermal cracking of the latter to vinyl chloride. To date, no industrial application of a one-step process is available. To close this gap, this work evaluates a wide range of self-prepared supported CeO2 and EuOCl catalysts for one-step production of vinyl chloride from ethylene in a fixed-bed reactor at 623 773 K and 1 bar using feed ratios of C2H4:HCl:O2:Ar:He = 3:3 6:1.5 6:3:82 89.5. Among all studied systems, CeO2/ZrO2 and CeO2/Zeolite MS show the highest activity but suffer from severe combustion of ethylene, forming COx, while 20 wt.% EuOCl/γ-Al2O3 leads to the best vinyl chloride selectivity of 87% at 15.6% C2H4 conversion with complete suppression of CO2 formation and only 4% selectivity to CO conversion for over 100 h on stream. Characterization by XRD and EDX mapping reveals that much of the Eu is present in non-active phases such as Al2Eu or EuAl4, indicating that alternative synthesis methods could be employed to better utilize the metal. A linear relationship between conversion and metal loading is found for this catalyst, indicating that always part of the used Eu is available as EuOCl, while the rest forms inactive europium aluminate species. Zeolite-supported EuOCl slightly outperforms EuOCl/γ Al2O3 in terms of total yield, but is prone to significant coking and is unstable. Even though a lot of Eu seems locked in inactive species on EuOCl/γ Al2O3, these results indicate possible savings of nearly 16,000 USD per kg of catalyst compared to a bulk EuOCl catalyst. These very promising findings constitute a crucial step for process intensification of polyvinyl chloride production and exploring the potential of supported EuOCl catalysts in industrially-relevant reactions.
Project 2 Abstract: Alkyne Semihydrogenation
Despite strongly suffering from poor noble metal utilization and a highly toxic selectivity modifier (Pb), the archetypal catalyst applied for the three-phase alkyne semihydrogenation, the Pb-doped Pd/CaCO3 (Lindlar catalyst), is still being utilized at industrial level. Inspired by the very recent strategies involving the modification of Pd with p-block elements (i.e., S), this work extrapolates the concept by preparing crystalline metal phosphides with controlled stoichiometry. To develop an affordable and environmentally-friendly alternative to traditional hydrogenation catalysts, nickel, a metal belonging to the same group as Pd and capable of splitting molecular hydrogen has been selected. Herein, a simple two-step synthesis procedure involving nontoxic precursors was used to synthesize bulk nickel phosphides with different stoichiometries (Ni2P, Ni5P4, and Ni12P5) by controlling the P:Ni ratios. To uncover structural and surface features, this catalyst family is characterized with an array of methods including X-ray diffraction (XRD), 31P magic-angle nuclear magnetic resonance (MAS-NMR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). Bulk-sensitive techniques prove the successful preparation of pure phases while XPS analysis unravels the facile passivation occurring at the NixPy surface that persists even after reductive treatment. To assess the characteristic surface fingerprints of these materials, Ar sputtering was carried out at different penetration depths, reveling the presence of Ni+ and P-species. Continuous-flow three-phase hydrogenations of short-chain acetylenic compounds display that the oxidized layer covering the surface is reduced under reaction conditions, as evidenced by the induction period before reaching the steady state performance. To assess the impact of the phosphidation treatment on catalytic performance, the catalysts were benchmarked against a commercial Ni/SiO2-Al2O3 sample. While Ni/SiO2-Al2O3 presents very low selectivity to the alkene (the selectivity is about 10% at full conversion) attributed to the well-known tendency of naked nickel nanoparticles to form hydrides, the performance of nickel phosphides is highly selective and independent of P:Ni ratio. In line with previous findings on PdxS, kinetic tests indicate the occurrence of a dual-site mechanism where the alkyne and hydrogen do not compete for the same site.
This work is the subject of a publication of which I am a co-author, as cited below.
D. Albani; K. Karajovic; B. Tata; Q. Li; S. Mitchell; N. López; J. Pérez-Ramírez. Ensemble Design in Nickel Phosphide Catalysts for Alkyne Semi-Hydrogenation. ChemCatChem 2019. doi.org/10.1002/cctc.201801430
Since the 1980’s, there has been a growing interest in the concept of sustainability. The prime directive of sustainability is to balance the needs of economics, environmental health, and human society. The change in the global climate, loss of biodiversity, increased levels of pollution, and general trend toward resource scarcity have all increased the momentum of the contemporary sustainability movement. Simultaneously, poverty and nutrition scarcity have attracted many to sustainability’s principles of resource equity. What one can gather from the diversity of sustainability’s intended functions is that it’s meant to solve several problems at once. In another sense, the most impactful sustainability solutions are multipurpose. This is not to say that any given solution is a panacea. On the contrary, sustainability advocates often dispute the existence of so-called “silver bullets” for these global issues. While this tends to reign true, it does not stop policy makers, communities, or researchers from attempting to employ multifaceted solutions. One such example is the myriad of sustainability issues associated with industrial agriculture. With the compounding issues of high water consumption, habitat destruction via land use change, biodiversity loss and climate change, industrial agriculture appears to be a damaging system. Areas like Arizona are projected to be affected by many of these issues. It thus stands to reason that if Arizona is to aggressively address its long-term drought, as well as global sustainability issues, a systematic change in farming practices needs to be made. Firstly, an analysis of the agricultural and water histories of Arizona will highlight the events most relevant to the region’s contemporary issues. Following this, the analysis will frame the greater problem through specific pieces of evidence associated with water scarcity in Arizona. Then, a summary of findings will illustrate the fundamental theories surrounding regenerative agriculture and three of its alternative forms: permaculture, dryland farming, and carbon farming. These theories will be instrumental in recommending a useful conception of regenerative agriculture for Arizona; it will be known as a Regenerative Dryland Farming System (RDFS). The extent and utility of current solutions will then be explored. The remainder of the section will illustrate the principles of the RDFSs, explore their potential weaknesses, and recommend policy for their successful deployment. Overall, it will be argued that RDFSs should fully replace industrial agriculture in Arizona. This will be vital in addressing the nine planetary boundaries and freshwater reality of the region.