A highly-sensitive ammonia (NH3) gas sensor based on molybdenum trioxide nanoribbons was developed in this study. α-MoO3 nanoribbons (MoO3 NRs) were successfully synthesized via a hydrothermal method and systematically characterized using various advanced technologies. Following a simple drop-cast process, a high-performance chemiresistive NH3 sensor was fabricated through the deposition of a MoO3 NR sensing film onto Au interdigitated electrodes. At an optimal operation temperature of 450 °C, the MoO3 nanoribbon-based sensor exhibited an excellent sensitivity (0.72) at NH3 concentration as low as 50 ppb, a fast response time of 21 s, good stability and reproducibility, and impressive selectivity against the interfering gases such as H2, NO2, and O2. More importantly, the sensor represents a remarkable limit of detection of 280 ppt (calculated based on a signal-to-noise ratio of 3), which makes the as-prepared MoO3 NR sensor the most sensitive NH3 sensor in the literature. Moreover, density functional theory (DFT) simulations were employed to understand the adsorption energetics and electronic structures and thus shed light on the fundamentals of sensing performance. The enhanced sensitivity for NH3 is explicitly discussed and explained by the remarkable band structure modification because of the NH3 adsorption at the oxygen vacancy site on α-MoO3 nanoribbons. These results verify that hydrothermally grown MoO3 nanoribbons are a promising sensing material for enhanced NH3 gas monitoring.

Adsorptive desulfurization with Cu and Ce ion-exchanged Y zeolite (CuCeY) has proven to be an effective method for the removal of sulfur compounds from hydrocarbon fuels. In this study, Cu and Ce exchanged Y materials including CuY, CeY, and CuCeY were prepared and examined to investigate the mechanism behind the superior sulfur adsorption and selectivity of CuCeY. In situ conditions were used to study the materials as prepared for optimal desulfurization. X-ray diffraction (XRD) confirmed the absence of large well-ordered crystalline phases from metallic or oxide Cu and Ce after the reduction of the samples. The oxidation states and local environments of Cu and Ce were determined using X-ray adsorption fine structure (XAFS) analysis and correlated to theoretical findings obtained from density functional theory (DFT) calculations. XAFS data indicate the successful reduction of Cu species to Cu + and Cu 0 , and Ce to Ce 3+ . Analysis of XAFS spectra located Cu and Ce within the Y zeolite framework with Cu cations in the six-member ring sites and as small metallic Cu clusters. Ce cations were found to occupy both sixmember ring and hexagonal prism sites. These results reveal the structure of CuCeY as prepared for desulfurization and provide insight into its superior sulfur adsorption performance.

Adsorptive desulfurization is a promising alternative to hydrodesulfurization for minimizing harmful sulfur emissions from hydrocarbon fuels. Cu in Y zeolite (CuY) has shown effective sulfur adsorption, especially when paired with Ce (CuCeY). This study explores other rare earths (REs), including La, Sm, and Nd, in RE and CuRE Y and mesoporous Y (SAY) zeolites for the adsorption of benzothiophene (BT) and dibenzo­thiophene (DBT). Metal loadings on the zeolites were quantified by using inductively coupled plasma optic emission spectroscopy (ICP-EOS) and X-ray fluorescence (XRF). Characteristic adsorption modes, such as σ-bonding and π-complexation, were observed by using Fourier-transform infrared spectroscopy (FTIR). X-ray diffraction (XRD) Rietveld refinement determined that RE ions prefer the sodalite cages of Y zeolite, while Cu occupies supercage sites. Ce showed the strongest synergy with Cu compared to the other REs and the highest adsorption capacity. The results of this study provide insight into the role of RE exchanged Y on sulfur adsorption.

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