Nonthermal plasmas (NTPs) produce reactive chemical environments, including electrons, ions, radicals, and vibrationally excited molecules, that can drive chemistry at temperatures at which such species are thermally inaccessible. There has been growing interest in the integration of conventional catalysis with reactive NTPs to promote novel chemical transformations. Unveiling the full potential of plasma-catalytic processes requires a comprehensive understanding of plasma-catalytic synergies, including characterization of plasma-catalytic surface interactions. In this work, we report on a newly designed multimodal spectroscopic instrument combining polarization-modulation infrared reflection-absorption spectroscopy (PM-IRAS), mass spectrometry, and optical emission spectroscopy (OES) for the investigation of plasma–surface interactions such as those found in plasma catalysis. In particular, this tool has been utilized to correlate plasma-phase chemistry with both surface chemistry and gas-phase products in situ (1) during the deposition of carbonaceous surface species via NTP-promoted nonoxidative coupling of methane and (2) during subsequent activation of surface deposits with an atmospheric pressure and temperature argon plasma jet on both nickel (Ni) and silicon dioxide (SiO2) surfaces. For the first time, the activation of carbonaceous surface species by a NTP on Ni and SiO2 surfaces to form hydrogen gas and C2 hydrocarbons was directly observed, where both PM-IRAS and OES measurements suggest that they may form through different pathways. This unique tool for studying plasma–surface interactions could enable more rational design of plasma-stimulated catalytic processes.

We describe a microfluidic approach to optimize crystallization of active pharmaceutical ingredients (APIs) and their solid forms (cocrystals) via crystal seeding. Subsequent on-chip X-ray diffraction is used to verify the crystal from. The microfluidic platform comprises an 8 × 9 well array that enables screening of seeding conditions (dilutions) by metering of API solution or API/cocrystal former solution and seed solution in ratios of 1:4 to 4:1, respectively, across each row. Slow solvent evaporation leads to seed growth and results in isolated diffraction quality crystals. To validate this microfluidic crystal seeding approach, three APIs (piroxicam, piracetam, and carbamazepine) and a cocrystal (carbamazepine/4-hydroxybenzoic acid) were used as model compounds. X-ray diffraction data was collected on-chip at room temperature to determine the crystal structure of the model compounds for comparison to published structural data. This on-chip seeding approach aided in crystallization of a desired solid form (e.g., a specific polymorph) over a mixture of solid forms. Easy handling, automated seeding and dilution, high throughput screening using small quantities of API (about 5 μg/well), and on-chip X-ray analysis of multiple crystals makes this platform attractive for solid form identification and characterization.

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