Microreactor-chip: The fused-silica glass chips used in this study as packed-bed microreactors were manufactured by an inhouse method, using a selective laser-induced etching (SLE) process, wafer-to-wafer alignment, and direct glass-glass bonding, followed by a high-temperature fusion bonding step of two structured wafers with subsequent chip dicing. The chip layout was created using CAD-software Autodesk Inventor Professional 2019 (San Rafael, CA, USA) and converted with CAM-software (Alphacam 2017 R2, Vero Software GmbH, Neu-Isenburg, DE) into a corresponding toolpath for the SLE-device (FEMTOprint f200 aHead P2, Muzzano, CHE). An ultrashort pulsed IR-laser (1030 nm, 400 fs, 230 nJ) was employed to structure the design onto a 4-inch fused silica wafer (thickness 1 mm), followed by a wet chemical-etching step in hot potassium hydroxide solution (8 M, 85 °C, 6 h). A detailed description of the manufacturing process can be found in the ESI in section S1.1. As shown in Fig. A, the chip design consists of multiple adjacent reactor channels located directly after the chip inlets. Each channel features a semi-circular reactor-bed (measured 76 x 26 x 2 mm; e.g., 15 reactor channels, each with 19 mm length, 150 µm width, and 65 µm depth, resulting in an empty reactor volume of approx. 265 nl and 132 nl packed). Each reactor channel can be separately filled with particulate material and terminates in an integrated weir-structure or µfrit, which retains the packed particles via the keystone effect (similar as we previously presented, µfrit shown in Fig. C, µfrit channels measuring 150 µm in length, 15-20 µm in width and depth). Beyond the weir-structure, there is an additional short channel (0.9 mm) before reaching the chip outlet. The conical inlet and outlet holes of the channels can be connected by utilising a custom-built high-pressure steel clamp system, allowing for a world-to-chip connection. The prepared packed-bed flow reactor can then be directly integrated into the fluidic setup by connection to the reactant feed. For reusability, the weirstructure is positioned on only one side of the chip, enabling reactor operation in a single direction and the possibility of subsequent reactor recycling by flushing the reactor in the opposite direction. This allowed for efficient removal of the particulate material and facilitated the repacking of the reactor with different materials.