Assessment of Waste-to-Energy Catalysts in Urban Refuse-Derived Fuel Streams for Emissions Reduction

Thesis Abstract

Urban refuse-derived fuel (RDF) streams present significant opportunities for energy recovery but are uncertainly aligned with emissions reduction goals due to catalyst performance variability and feedstock heterogeneity. This study addresses the problem of optimizing waste-to-energy (WtE) catalytic processes to minimize airborne pollutants while maintaining energy efficiency in urban RDF-fired systems. The aim is to evaluate catalyst performance and identify operational conditions that maximize NOx, SOx, and toxic particulate emissions reductions without compromising energy output. Specific objectives include (i) characterizing RDF composition and contaminant profiles across three urban collection districts (n=120 feedstock samples over 12 months); (ii) assessing the activity, selectivity, and deactivation rates of three commercially available and two novel catalysts (field-tested in pilot-scale reactors) under realistic RDF-derived gas compositions; (iii) quantifying emissions reductions using in-situ monitoring coupled with laboratory validation; (iv) developing a process-optimization framework linking catalyst type, operating parameters, and emissions outcomes; and (v) formulating guidelines for catalyst selection and maintenance for municipal WtE facilities. Methodologically, the study adopts a mixed-methods empirical design grounded in systems theory and the technology acceptance framework. The population comprises municipal WtE plants and associated RDF streams in a mid-sized metropolitan region. A stratified sampling scheme yields 60 RDF bulk samples for feedstock characterization and 5 pilot-scale reactor runs per catalyst group, totaling 25 runs. Data collection integrates (a) feedstock analysis via proximate and ultimate analyses, calorific value measurements, and trace metal screening using inductively coupled plasma mass spectrometry (ICP-MS); (b) catalyst performance data recorded through online gas chromatography–mass spectrometry (GC-MS) for volatile inorganic and organic emissions, Fourier-transform infrared spectroscopy (FTIR) for real-time gas species, and differential scanning calorimetry (DSC) for catalyst thermal properties; (c) emissions measurements validated by extractive sampling and gravimetric PM analysis using a tapered element oscillating microbalance (TEOM); and (d) process parameters captured from plant control systems. Validity and reliability are ensured through calibration with certified standards, triplicate analyses, and inter-laboratory cross-checks. Data analysis employs a combination of regression analysis to model emissions as a function of catalyst type, RDF composition, and operating temperature; ANOVA to assess differences among catalyst groups; response surface methodology (RSM) to optimize operating conditions; and multivariate techniques (principal component analysis) to relate feedstock variability to emissions outcomes. A mechanistic kinetic model is developed to describe catalyst deactivation and sulfur/oxidation pathways under RDF-derived gas matrices. Expected findings include (i) quantified reductions in NOx (up to 40–60%), SOx (30–50%), and particulate emissions with select catalysts under optimized temperatures (650–750°C) and metal loadings; (ii) identification of RDF compositional factors (chlorine, heavy metal content, moisture) that most strongly influence catalyst performance and deactivation; (iii) evidence that catalyst regeneration cycles extend operational life without compromising emissions performance; and (iv) a robust optimization model linking catalyst design, reactor conditions, and emissions outcomes, validated by a cross-validation dataset (n=15). The study contributes to knowledge by integrating RDF heterogeneity, catalyst performance dynamics, and operational optimization into a coherent framework for WtE emissions management. It advances practical understanding of catalyst selection criteria, maintenance scheduling, and feedstock preprocessing requirements for city-scale RDF-to-energy facilities. The main conclusion anticipates that a targeted combination of catalyst type and precisely tuned reactor conditions can achieve substantial emissions reductions across urban RDF streams while maintaining energy efficiency, with explicit recommendations for catalyst choice, pre-treatment of RDF, and monitoring strategies. Policy implications include guidance for regulatory compliance and reporting standards for WtE plants, while operational guidelines propose a decision-support tool enabling municipal facilities to customize catalyst strategies based on RDF characteristics and plant capacity. Recommendations for further research encompass long-term field trials across diverse urban contexts, exploration of novel catalysts with enhanced sulfur tolerance, and lifecycle assessment to quantify environmental trade-offs of catalyst deployment in WtE systems.