Although considerable progress has been made in direct synthesis gas (syngas) conversion to light olefins (C2(=)-C4(=)) via Fischer-Tropsch synthesis (FTS), the wide product distribution remains a challenge, with a theoretical limit of only 58% for C2-C4 hydrocarbons. We present a process that reaches C2(=)-C4(=) selectivity as high as 80% and C2-C4 94% at carbon monoxide (CO) conversion of 17%. This is enabled by a bifunctional catalyst affording two types of active sites with complementary properties. The partially reduced oxide surface (ZnCrO(x)) activates CO and H2, and C-C coupling is subsequently manipulated within the confined acidic pores of zeolites. No obvious deactivation is observed within 110 hours. Furthermore, this composite catalyst and the process may allow use of coal- and biomass-derived syngas with a low H2/CO ratio.

The discovery of superconductivity at 39 K in MgB 2 1 raises many issues. One of the central questions is whether this new superconductor resembles a hightemperature-cuprate superconductor or a lowtemperature metallic superconductor in terms of its current carrying characteristics in applied magnetic fields. In spite of the very high transition temperatures of the cuprate superconductors, their performance in magnetic fields has several drawbacks 2 . Their large anisotropy restricts high bulk current densities to much less than the full magnetic field-temperature (H-T) space over which superconductivity is found. Further, weak coupling across grain boundaries makes transport current densities in untextured polycrystalline forms low and strongly magnetic field sensitive 3,4 . These studies of MgB 2 address both issues. In spite of the multi-phase, untextured, nano-scale sub-divided nature of our samples, supercurrents flow throughout without the strong sensitivity to weak magnetic fields characteristic of Josephson-coupled grains 3 . Magnetization measurements over nearly all of the superconducting H-T plane show good temperature scaling of the flux pinning force, suggestive of a current density determine d by flux pinning. At least two length scales are suggested by the magnetization and magneto optical (MO) analysis but the cause of this seems to be phase inhomogeneity, porosity, and minority insulating phase such as MgO rather than by weakly coupled grain boundaries. Our results suggest that polycrystalline ceramics of this new class of superconductor will not be compromised by the weak link problems of the high temperature superconductors, a conclusion with enormous significance for applications if higher temperature analogs of this compound can be discovered.The principal samples were synthesized by direct reaction of bright Mg flakes (Aldrich Chemical) and sub-micron amorphous B powder (Callery Chemical). Starting materials were lightly mixed in half-gram batches, and pressed into pellets. These pellets were placed on Ta foil, which was in turn placed on Al 2 O 3 boats, and fired in a tube furnace under a mixed gas of 95% Ar 5% H 2 for 1 hour at 600 C, 1 hour at 800 C, and 1 hour at 900 C, and then lightly ground. The resulting powders were pressed into pellets and then hot pressed at 10 kbar at temperatures between 650 and 800 °C for periods between 1 and 5.5 hours. Disks ~4 mm in diameter and ~1 mm thick were cut from these pellets for property characterization. As noted later, this process cannot yet be considered optimum.Magnetization properties were examined in SQUID and vibrating sample magnetometers (VSM) in applied fields up to 14 T from 4.2 to above T c . Figure 1 shows onset T c values of 37-38 K for the above samples and for commercial MgB 2 powder (99.5%, ~2 µm diameter by examination, CERAC). Sample 1 and the commercial powder show smooth transitions with some temperature dependence of the zerofield cooled (ZFC) shielded moment, while sample 3 exhibits a step, indicative of non-uniformity in su...

The interplay of magnetic interactions, the dimensionality of the crystal structure and electronic correlations in producing superconductivity is one of the dominant themes in the study of the electronic properties of complex materials. Although magnetic interactions and two-dimensional structures were long thought to be detrimental to the formation of a superconducting state, they are actually common features of both the high transition-temperature (Tc) copper oxides and low-Tc material Sr2RuO4, where they appear to be essential contributors to the exotic electronic states of these materials. Here we report that the perovskite-structured compound MgCNi3 is superconducting with a critical temperature of 8 K. This material is the three-dimensional analogue of the LnNi2B2C family of superconductors, which have critical temperatures up to 16 K (ref. 2). The itinerant electrons in both families of materials arise from the partial filling of the nickel d-states, which generally leads to ferromagnetism as is the case in metallic Ni. The high relative proportion of Ni in MgCNi3 suggests that magnetic interactions are important, and the lower Tc of this three-dimensional compound-when compared to the LnNi2B2C family-contrasts with conventional ideas regarding the origins of superconductivity.