Milling Down to Nanometers: A General Process for the Direct Dry Synthesis of Supported Metal Catalysts

Abstract

Supported catalysts are among the most important classes of catalysts.T hey are typically prepared by wetchemical methods,s uch as impregnation or co-precipitation. Here we disclose that dry ball milling of macroscopic metal powder in the presence of asupport oxide leads in many cases to supported catalysts with particles in the nanometer size range.V arious supports,i ncluding TiO 2 ,A l 2 O 3 ,F e 2 O 3 ,a nd Co 3 O 4 ,a nd different metals,s uch as Au,P t, Ag,C u, and Ni, were studied, and for eacho ft he supports and the metals, highly dispersed nanoparticles on supports could be prepared. The supported catalysts were tested in CO oxidation, where they showed activities in the same range as conventionally prepared catalysts.T he method thus provides as imple and cost-effective alternative to the conventionally used impregnation methods.

Mechanochemical Synthesis of Catalytic Materials

“…Operation at temperatures ranging from −196 °C to 150 °C was achieved in grinding jars equipped with appropriate temperature control (e.g., a cryostat or a heating box) [28–30] . Moreover, the grinding jar can be modified for processing under a controlled atmosphere, both in static (pressure) [31–33] and dynamic (flow‐through) conditions, [34–38] which remarkably extends the field of application of mechanochemistry.…”

“…The NPs are synthesized mainly by wet‐chemistry and thermal methods, including precipitation, sol‐gel synthesis, hydrothermal synthesis, spray drying, annealing, and flame pyrolysis, to mention only a few [39, 41] . The mechanochemical route, which is becoming more and more popular, [14–15, 37, 42] already proved to be advantageous over conventional methods as a low‐waste or even waste‐free process. Besides, the availability of high‐energy ball milling devices (see Section 2), which typically have 1000 times higher impact energy than conventional ball mills, enable access to sub‐micrometre to nanometre‐sized solid particles [43–44] .…”

“…Besides, the availability of high‐energy ball milling devices (see Section 2), which typically have 1000 times higher impact energy than conventional ball mills, enable access to sub‐micrometre to nanometre‐sized solid particles [43–44] . This is a notable advancement compared to conventional milling devices, which indeed already allowed access to the domain (crystallite) size in the nanometre range, but not to particle sizes of the same order of magnitude, as they typically lie in the micrometre range [37, 45] . In any case, the reports on the mechanochemical synthesis of nanoparticles should be interpreted with caution.…”

Current Strategies for Noble Metal Nanoparticle Synthesis

“…In mechanical milling, the kinetic energy of the rollers/balls is transferred to the bulk material, which results in the reduction in grain size [ 87 ]. Parameters such as the type of mill, milling atmosphere, milling media, intensity, time and temperature play a crucial role in controlling the shape and size of the NPs [ 88 , 89 ]. Different techniques have been developed in order to overcome these constraints, including shaker mills, tumbler mills, vibratory mills, attrition mills and planetary mills.…”

Simple physical mixing of zeolite prevents sulfur deactivation of vanadia catalysts for NOx removal

“…The advantage of this system is that, unlike with stable metal sulfates, the unstable ammonium sulfate (ABS) salts can be decomposed at low temperatures, making the system reusable upon regeneration at temperatures as low as 350 °C. In addition, simple physical mixing approach is a cost-effective and practical solution that can be easily applied to the industry 25 . This catalyst-protection system enables low-temperature operation of NH 3 -SCR in industrial plants, which has been impossible due to the above-described stability issues.…”