Physical mixture

Polymer alloys are physical mixtures of structurally different homopolymers or copolymers. The mixture is held together by secondary intermolecular forces such as dipole interaction, hydrogen bonding, or van der Waals forces. 

The treatments used to recover nickel from its sulfide and lateritic ores differ considerably because of the differing physical characteristics of the two ore types. The sulfide ores, in which the nickel, iron, and copper occur in a physical mixture as distinct minerals, are amenable to initial concentration by mechanical methods, eg, flotation (qv) and magnetic separation (see SEPARATION,MAGNETIC). The lateritic ores are not susceptible to these physical processes of beneficiation, and chemical means must be used to extract the nickel. The nickel concentration processes that have been developed are not as effective for the lateritic ores as for the sulfide ores (see also Metallurgy, extractive Minerals recovery and processing). 

Catalysts from Physical Mixtures. Two separate catalysts with different functions may be pulverized to fine powders and mixed to form a catalyst system that accomplishes a reaction sequence that neither of the two iadividual catalysts alone can achieve. For such catalyst systems, the reaction products of catalyst A become the feedstocks for catalyst B and vice versa. An example is the three-step isomerization of alkanes by a mixture of... 

A variety of mixed metal catalysts, either as fused oxides (42 7 8) or coprecipitated on supports (25 0) or as physical mixtures of separate catalysts (5P), have been tested in aniline reductions. In the hydrogenation of ethyl p-aminobenzoate, a coprccipitated 3% Pd, 2% Rh-on-C proved superior to 5% Rh-on-C, inasmuch as hydrogenolysis to ethyl cyclohexanecarboxylate was less (61) (Table 1). 

The catalytic pyrolysis of R22 over metal fluoride catalysts was studied at 923K. The catalytic activities over the prepared catalysts were compared with those of a non-catalytic reaction and the changes of product distribution with time-on-stream (TOS) were investigated. The physical mixture catalysts showed the highest selectivity and yield for TFE. It was found that the specific patterns of selectivity with TOS are probably due to the modification of catalyst surface. Product profiles suggest that the secondary reaction of intermediate CF2 with HF leads to the formation of R23. 

Aluminum fluoride (AIF3), calcium fluoride (CaF2) and their physical mixture (denoted as Mixed hereafter for abbreviation) were prepared. The amount of copper was adjusted to be 10 wt.%. The reaction was carried out in the fixed-bed reaction system under the reaction temperature of 923 K, space velocity of 15,000 h, 10% R22 in N2-balacne and atmospheric... 

Figure 1. UV-visible spectra of (a) physical mixture of NaY and the chloride salt of 1, (b) Mo/NaY, (c) Mo/HUSY and (d) Mo/KL.

Fig. 2 Change of the acid sites on the physical mixture of Pt/ Si02 and H-ZSM-5 with hydrogen treatment and the following outgassing.

Fig. 7 Cumene cracking over H-ZSM5 and the physical mixture of Pt/Si02 and H-ZSM-5 at 423K in a pulse reactor.

Yang et al. found that Ag-core/Pt-shell nanoparticles with a core/shell could only be formed by the successive reduction method using Ag nanoparticles as the seeds. Results of measurements of UV-Vis, TEM, EDX, and XPS supported the core/shell structure of the bimetallic nanoparticles. The reverse order of preparation using Pt nanoparticles as the seeds did not provide any core/shell nanoparticles while a physical mixture of Ag nanoparticles and the original Pt seeds was obtained [140]. 

Figure 5. Plausible formation mechanism of core/shell structured bimetallic nanoparticles by a physical mixture. (Reprinted from Ref [146], 2005, with permission from American Chemical Society.)...

Figure 11. X-ray diffraction patterns of PVP-protected metal nanoparticles (a) PVP-protected CuPd (Cu Pd = 2 1) bimetallic nanoparticles (b) PVP-protected Pd nanoparticles (c) PVP-protected Cu dispersion (d) physical mixture of (b) and (c) (Cu Pd = 2 1). (Reprinted from Ref [71], 1993, with permission from The Chemical Society of Japan.)...

The XRD and TEM showed that the bimetallic nanoparticles with Ag-core/Rh-shell structure spontaneously form by the physical mixture of Ag and Rh nanoparticles. Luo et al. [168] carried out structure characterization of carbon-supported Au/Pt catalysts with different bimetallic compositions by XRD and direct current plasma-atomic emission spectroscopy. The bimetallic nanoparticles were alloy. Au-core/Pd-shell structure of bimetallic nanoparticles, prepared by co-reduction of Au(III) and Pd(II) precursors in toluene, were well supported by XRD data [119]. Pt/Cu bimetallic nanoparticles can be prepared by the co-reduction of H2PtClg and CuCl2 with hydrazine in w/o microemulsions of water/CTAB/ isooctane/n-butanol [112]. XRD results showed that there is only one peak in the pattern of bimetallic nanoparticles, corresponding to the (111) plane of the PtCu3 bulk alloy. 

Physical mixtures consist of reversibly crosslinked and uncrosslinked hydrocolloid compositions and hydrocolloids. These show improved dispersion properties [1708]. 

Another example of performance enhancement using a zeolite/TUD-1 catalyst is shown in n-hexane cracking using a series of zeolite-Beta-embedded TUD-1 catalysts (29) 20, 40 and 60 wt% zeolite Beta in Al-Si-TUD-1 (Si/Al = 150). These are compared to pure zeolite Beta, and to a physical mixture of 40% zeolite Beta and 60% Al-Si-TUD-1. These catalysts were tested in a fixed bed reactor, at atmospheric pressure, with constant residence time at 538°C. The pseudo-first-order rate constants are shown in Figure 41.8. Note that the zeohte-loaded catalysts were clearly superior to both the pure zeolite Beta catalyst and the zeohte-TUD-1 physical mixture. Again, this is evidence that catalyst performance benefits from a hierarchical pore stracture such as zeolite embedded in TUD-1. 

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