The miniaturization of mechanical devices calls for novel solutions to reduce frictional effects in regimes where standard lubrication approaches fail. Particularly promising for applications in nano- and micro-motive components are the lubrication properties displayed by rigid layered materials. Among the latter, graphene and hexagonal boron-nitride (h-BN) stand out for their extraordinary mechanical properties that can provide the required interfacial robustness and durability. Furthermore, their intrinsic intra-layer lattice mismatch foreshadows the possibility to realize superlubric heterojunctions made thereof. To achieve microscopic understanding of the underlying tribological processes we perform fully atomistic molecular mechanics simulations of the sliding friction at graphene/h-BN interfaces. For the aligned heterojunctions we find a characteristic contact size, above which superlubricity sets in due to the progressive appearance of the Moiré pattern. Incommensurability effects are enhanced in misaligned contacts, and kinetic friction is found to further reduce by orders of magnitude. Our simulations also show that the superlubric regime in graphene/h-BN heterostructures persists up to significantly higher loads compared to the well-studied twisted homogeneous graphene interface. This indicates the potential for achieving robust superlubricity in practical applications using two-dimensional layered materials heterojunctions.