Abstract
In this paper we report a new nanometallic, self-activating catalyst, namely, Ni-supported Pd nanoparticles (PdNPs/Ni) for low temperature ammonia cracking, which was prepared using a novel approach involving the transfer of nanoparticles from the intermediate carrier, i.e. nano-spherical SiO2, to the target carrier technical grade Ni (t-Ni) or high purity Ni (p-Ni) grains. The method that was developed allows a uniform nanoparticle size distribution (4,4±0.8 nm) to be obtained. Unexpectedly, the t-Ni-supported Pd NPs, which seemed to have a surface Ca impurity, appeared to be more active than the Ca-free (p-Ni) system. A comparison of the novel PdNPs/Ni catalyst with these reported in the literature clearly indicates the much better hydrogen productivity of the new system, which seems to be a highly efficient, flexible and durable catalyst for gas-phase heterogeneous ammonia cracking in which the TOF reaches a value of 2615 mmolH2/gPd min (10,570 molNH3/molPd(NP) h) at 600°C under a flow of 12 dm3/h (t-Ni).
Highlights
Ammonia cracking is a method that is used in the treatment of flue gases from coal or biomass gasification or for hydrogen generation in chemical or related industries
After 10 min of stirring, 60 mL of tetraethyl orthosilicate was added to the reaction mixture, which was stirred for 3 h at room temperature
The average sizes of the supported Pd nanoparticles were determined by analyzing data from different transmission electron microscopy (TEM) (Fig 1D) images, and showed an average diameter of 4.4 ± 0.8 nm
Summary
Ammonia cracking is a method that is used in the treatment of flue gases from coal or biomass gasification or for hydrogen generation in chemical or related industries. It is an important issue in hydrogen economy. Ammonia decomposition is a complex process that proceeds through a stepwise dehydrogenation that yields H and N, which recombine into H2 and N2, respectively. The binding energy of the nitrogen must be sufficiently strong for dehydrogenation, it should not be so high that it blocks the recombination step [3,4,5]
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